Four mainly starting a 115HP 4 stroke, what is the difference between a $100 battery and a $400 battery? This is a recreational boat, with a battery charger installed on boat. Boat also has a 9.8 kicker that has its own fuel line to main tank. It’s a pull start. One Garmin fish finder, and stereo.
Side bonus question:
Wouldn’t doubling up on two $100 batteries with a switch be better than one of the $400 batteries?
And the double or nothing side bonus question:
What battery do you recommend for the above application?
I like the Optima Yellow about $300, & it’s all about reliability & long cranking ability during engine troubles, for me, in Marine or “ far from anywhere” four-wheeling.
A lot depends on that battery under those conditions.
I also like Bass Pro Shop’s wool blend Redhead socks.
Is Buying A Cheap Marine Battery Worth it? At one time or another, every boater will have to purchase a battery. At some point during their time shopping around, looking at different types and different prices, they will all ask whether they should go with top of the line or a more value priced battery. Some choose pricy while others choose cheap. Are you curious about whether buying a cheap marine battery worth it? There are pros and cons with each choice, but here is what will make a difference between satisfaction and disappointment.
Choosing a High End Marine Battery There are reasons you should choose to spend more on a top of the line marine battery. However, many people simply do not want or have the money to spend. Some can cost as much as 2, 3, or 4 times the amount of a cheap battery. However, by paying more up front, most people can expect a much longer lifespan. This is a good example of it saving you money in the long run. With that being said, though, even the best battery on the market can come up short if you are not able to take care of it properly. This is because high end does not always mean indestructible.
The Cheap Marine Battery When choosing cheap marine batteries, you have to go into it with the idea that you are not buying a battery that will last you 10 years. If you get a couple years out of it, you can feel as though you found a true value. It will still require maintenance to give it longevity, but it is possible in some cases to have a cheap battery last longer than most would expect. Cheap batteries can also mean throw-a-way batteries. You cannot purchase a cheap battery and really be surprised when you have to replace it three times as often as you have to replace the top dollar marine batteries on the market, but it does save you from having a huge initial investment on the battery.
Choosing the Middle Ground
Since there is such a broad range in battery prices, many people choose to opt for the middle ground. Those batteries that are not rock bottom cheap, but will not cost them an entire week’s pay, either. This is why people look for a marine battery sale so that they can get top dollar batteries for lower prices. It does take a little time to find marine batteries for sale and sometimes you may not have the time to search. If that is a situation you are in, you may consider one of the top choices for mid-range marine batteries. They are popular because they are longer lasting and more durable than a cheap battery, but not as expensive as the top dollar marine batteries.
If you’ve got an auxiliary motor, PLUS it’s a fishing boat (with at least one, if not two other batteries, for the trolling motor), then I don’t see why you’d need a $400 starting battery. You already have two extras to jump start off of, plus a backup motor.
Keep the $100 battery charged, and don’t let it sit out all winter. Replace every 3-4 years.
One cranking battery, two more for running electronics, live well, trolling motor, pumps, lights, ect.
That’s my philosophy. Of the ones I’ve run I rarely get more than 2-3 years out of them. I don’t know that it’s the best solution, I’ve used everything from Walmart brand to Interstate but mostly use Interstate because the local hardware store carries them.
Keep them on a charger when not in use and expect to replace them every couple of seasons.
A 115 horse fuel injected can get by with a 400-500 CCA marine starting battery and should be around the hundred dollar mark. It will run the radio and fish finder fine as long as its fully charged and still start the motor with 25 percent of its capacity.
The difference between the $100 and $400 dollar offerings is going to be composition. Traditional lead acid battery versus AGM or Lithium battery; the kicker is the on board charger. Its probably automatic, made for traditional lead acid (wet) batteries, which won't work well with the $400 dollar whiz bang (and unnecessary) AGM or Lithium batteries.
Doubling the $100 batteries, provided they are both fully charged, will provide more capacity than most need on a day on the water. It depends on the radio and locator use and their output, but spending more money for a different composition isnt going to double the output you can atrain with two traditional wet batteries.
Ive seen few need anything more than a standard group 24 lead acid battery (the $100 one) for their uses. What makes the biggest difference is the state of charge of the battery, regardless of composition.
My advice with onboard, automatic chargers is to run an initial charge, disconnect for 24 hours and connect again. Disconnect and repeat a day prior to use.
Is Buying A Cheap Marine Battery Worth it? At one time or another, every boater will have to purchase a battery. At some point during their time shopping around, looking at different types and different prices, they will all ask whether they should go with top of the line or a more value priced battery. Some choose pricy while others choose cheap. Are you curious about whether buying a cheap marine battery worth it? There are pros and cons with each choice, but here is what will make a difference between satisfaction and disappointment.
Choosing a High End Marine Battery There are reasons you should choose to spend more on a top of the line marine battery. However, many people simply do not want or have the money to spend. Some can cost as much as 2, 3, or 4 times the amount of a cheap battery. However, by paying more up front, most people can expect a much longer lifespan. This is a good example of it saving you money in the long run. With that being said, though, even the best battery on the market can come up short if you are not able to take care of it properly. This is because high end does not always mean indestructible.
The Cheap Marine Battery When choosing cheap marine batteries, you have to go into it with the idea that you are not buying a battery that will last you 10 years. If you get a couple years out of it, you can feel as though you found a true value. It will still require maintenance to give it longevity, but it is possible in some cases to have a cheap battery last longer than most would expect. Cheap batteries can also mean throw-a-way batteries. You cannot purchase a cheap battery and really be surprised when you have to replace it three times as often as you have to replace the top dollar marine batteries on the market, but it does save you from having a huge initial investment on the battery.
Choosing the Middle Ground
Since there is such a broad range in battery prices, many people choose to opt for the middle ground. Those batteries that are not rock bottom cheap, but will not cost them an entire week’s pay, either. This is why people look for a marine battery sale so that they can get top dollar batteries for lower prices. It does take a little time to find marine batteries for sale and sometimes you may not have the time to search. If that is a situation you are in, you may consider one of the top choices for mid-range marine batteries. They are popular because they are longer lasting and more durable than a cheap battery, but not as expensive as the top dollar marine batteries.
One cranking battery, two more for running electronics, live well, trolling motor, pumps, lights, ect.
That’s my philosophy. Of the ones I’ve run I rarely get more than 2-3 years out of them. I don’t know that it’s the best solution, I’ve used everything from Walmart brand to Interstate but mostly use Interstate because the local hardware store carries them.
Keep them on a charger when not in use and expect to replace them every couple of seasons.
The best solution is to get a hydrometer and learn how to use it instead of using an automatic charger.
I have 4 Walmart Batteries on board 1 for Cranking,2 Fish Finders and 3 batteries for 36V Trolling Motor.When i get back home from fishing the on board charger is plugged in and stays on all the time.Get 4-6 years on the Batteries.
Automatic chargers are limited to where they cutoff in voltage.
They aren't a panacea to not knowing jack about what ACTUAL state of charge your batteries are at, which is ONLY read from the specific gravity of the electroyte, NOT any open current voltage reading, which is the only thing automatic chargers operate by. Yes, an automatic charger can say 100% and put you on the water with a battery with a lot less, even less than 50%...
Last deep cycle I had was ten years old, still wasnt toast, but took a bit of goading to hit 1275-1300 specific gravity. The current one is seven.
Tournament fisherman won't see that type of annual life in a wet battery because they generally expire them cyclically.
If your starting motor is only used for starting, you really don't want a deep cycle marine battery for that purpose............a sealed, mid-range automotive battery is best.
For the other 2 batteries that run accessories, you do want marine deep cycle batteries.
There are only 2 real battery manufacturers left today, so no matter what "brand" is on it, it's made by one of those two.
Rule of thumb is $$$ = longevity, but not always in every case.
Best advice I have here is listen to Hawkl. From what I've read here he knows his shiet.
All I will say is that with what I've dealt with the last 10 years as far as boat batteries is take them in in the fall and put them on a trickle charger and check the water (distilled) in the spring when you take them out. I am currently running a sealed and an unsealed battery I bought with the boat 5 years ago and they both hold a charge well. Buy decent and take care of them and they'll be good to you from what I've seen.
My boat has four batteries, two with a switch for starting and running the electronics, and two more completely isolated from the boat's electrical system that are for the trolling motor.
Most saltwater boats will be set up with two starting batteries and use a switch like this one that allows you to choose battery 1 or battery 2 with a third position combining them in case you're having starting troubles. I use battery 1 for one day then battery 2 the next day, you don't use the combined position unless you're having trouble.
Two batteries are better than one for redundancy, I wouldn't want to take a boat with one starting battery very far away from land.
There are three general types of lead acid marine batteries, one meant only for starting, deep cycle batteries means for high draw things like trolling motors, and dual purpose batteries that are about halfway between the two. Mine are group 24 dual purpose types (group 24DC), they're for starting the motor and also run the electronics like the GPS/fishfinder, stereo, pumps, etc. The two trolling motor batteries are type 27 deep cycles (group 27DCX) and only run the trolling motor. My batteries, both the starting batteries and deep cycle batteries, are duracells from Sam's Club and I've been happy with them. They're about $80-90 each. The expensive batteries you mentioned are probably AGM or lithiums. Only you can decide if they're worth 4X the price, they're not to me.
Opinions vary but I'm of the opinion that the full time trickle chargers do more damage than anything. People complaining that their batteries don't last usually start their post with "the batteries have always been kept on a charger". I never charge my starting batteries unless it's the beginning of the year and the boat has been stored for the winter, the boat's charging system keeps them charged. My trolling motor batteries I charge fully when I get back from using them then again before taking it out if the boat has been sitting for more than a couple of weeks. I don't keep them on a constant charger.
What would I recommend for the OP's purposes? I'd recommend two dual purpose batteries 24DC batteries wired with one of the aforementioned switches, that'll keep you out of trouble and won't break the bank. Many of the high dollar designer batteries are overpriced junk.
Best advice I have here is listen to Hawkl. From what I've read here he knows his shiet.
All I will say is that with what I've dealt with the last 10 years as far as boat batteries is take them in in the fall and put them on a trickle charger and check the water (distilled) in the spring when you take them out. I am currently running a sealed and an unsealed battery I bought with the boat 5 years ago and they both hold a charge well. Buy decent and take care of them and they'll be good to you from what I've seen.
Thank you.
And here I thought all those years in the business was a waste!
Anyone with a hydrometer can verify state of charge or test how in-accurate their automatic charger is (EZ RED makes a nice, simple one). A battery reading 1275-1300 is good for three months if away from heat above 70 degrees and direct sun and won't freeze above -15 nor sulfate internally.
If its a wet battery and its sealed, it will need monitored with a voltmeter or charger by OCV readings away from surface charge.
My understanding is freshwater bass style boats usually run one battery that is in charge of starting and running the electronics. In addition, they run between one to three batteries for the trolling motor. These run only the trolling motor.
Most marine cranking batteries are likely ‘dual purpose’ because they also run the electronics. They are kind of a compromise between the thin plate high amp starting battery and thick plate durability of a deep cycle. If all you do is crank with your cranking battery, then I would think a regular crank battery would work fine. The trolling motor batteries would be best if they were true deep cycle, but I am sure some dual purpose batteries are used in this application as well.
As an aside, I carry a set of jumper cables in case I have to jump from my trolling motor batteries to my start battery. I haven’t had to do it yet but it is my backup plan. If you try this, make sure you understand how to hook up the jumpers so you don’t accidentally run 24V or 36V to your 12V starter and motor computer.
I had one of my two interstate trolling motors die after about 1.5 years. Always replace them in pairs (or threes if you have a 36V system). So...I wound up buying two replacements and kept the good battery for other uses.
One more thing, I believe a good carbon pile load tester is a pretty good investment for someone who had lots of batteries. It will help you sort out the wheat from the chaff regarding what’s good and what needs to be replaced.
Year 6 on my Costco Marine batteries (2 batteries setup). I take them out of the boat for winter and trickle charge (0.5 amp) once a month while inside. Think they cost a little north of a C-note.
I buy Walmart upper-end marine batteries they exchange them if they go bad. And have seen several fires with trickle chargers I make sure they are fused!!!
Had a fire on my boat from a solar charger regulator some one caught it in time burned my canvas top. Everything is fused now!
One more thing, I believe a good carbon pile load tester is a pretty good investment for someone who had lots of batteries. It will help you sort out the wheat from the chaff regarding what’s good and what needs to be replaced.
They're good for testing charged starting batteries, but won't help ideally with cycling batteries, which need cycled for a proper test.
You can also use them to detect a bad cell, but hydrometers are much safer. If one cell has 25-50 points variance, dont bother charging. It may kaboom if you do. With a load tester, any cell that percolates rapidly and emits gas is toast as well, but be aware that gas is highly flammable.
Best advice I have here is listen to Hawkl. From what I've read here he knows his shiet.
All I will say is that with what I've dealt with the last 10 years as far as boat batteries is take them in in the fall and put them on a trickle charger and check the water (distilled) in the spring when you take them out. I am currently running a sealed and an unsealed battery I bought with the boat 5 years ago and they both hold a charge well. Buy decent and take care of them and they'll be good to you from what I've seen.
Thank you.
And here I thought all those years in the business was a waste!
Anyone with a hydrometer can verify state of charge or test how in-accurate their automatic charger is (EZ RED makes a nice, simple one). A battery reading 1275-1300 is good for three months if away from heat above 70 degrees and direct sun and won't freeze above -15 nor sulfate internally.
If its a wet battery and its sealed, it will need monitored with a voltmeter or charger by OCV readings away from surface charge.
Newb boater here. And despite my profession, I'm a minimal maintenance guy on recreational stuff.
Are you saying that batteries shouldn't be kept in summer temps over 70 degrees? Common here to not see night time temps below 70 in summer.
Four mainly starting a 115HP 4 stroke, what is the difference between a $100 battery and a $400 battery? This is a recreational boat, with a battery charger installed on boat. Boat also has a 9.8 kicker that has its own fuel line to main tank. It’s a pull start. One Garmin fish finder, and stereo.
Side bonus question:
Wouldn’t doubling up on two $100 batteries with a switch be better than one of the $400 batteries?
And the double or nothing side bonus question:
What battery do you recommend for the above application?
Odyssey battery sized for your needs with a pro charger/dual pro battery charger. When not in use keep charger plugged in, going on 10 years with that set up in my boat. Cry once
I like your set-up, and I'm personally geared towards redundancy on any critical system.
Question... Could that battery selector switch, or something similar be used to connect to a trolling motor battery for an emergency start. Would doing so complicate the charging system? Also, would the 1&2 switch position work with different style batteries? (deep cycle and starting)
My boat is small, at 16'8", and I'm running a single battery for the 55 lb thrust trolling motor
Four mainly starting a 115HP 4 stroke, what is the difference between a $100 battery and a $400 battery? This is a recreational boat, with a battery charger installed on boat. Boat also has a 9.8 kicker that has its own fuel line to main tank. It’s a pull start. One Garmin fish finder, and stereo.
Side bonus question:
Wouldn’t doubling up on two $100 batteries with a switch be better than one of the $400 batteries?
And the double or nothing side bonus question:
What battery do you recommend for the above application?
In short, that $400 battery is a gel battery. They don't break as easy as a traditional battery, but it's pretty tough to break a traditional battery.
Extra batteries are never a bad thing, but weight becomes an issue on small boats.
I use Interstate (4) on my personal boat.
Optima on the dozen, or so, boats I drive on my other job. (I don't have to buy them.)
Year 6 on my Costco Marine batteries (2 batteries setup). I take them out of the boat for winter and trickle charge (0.5 amp) once a month while inside. Think they cost a little north of a C-note.
Same here. 2 Costco batteries get abused during the summer, sit all winter, then put on a charger in the spring. I’m surprised they’ve lasted the 4 or 5 years I’ve had them.
At this rate that $400 batterie better last 20 years.
I have a Walmart marine starting battery (around $90 last time I purchased) in my Ski boat, We typically get about 200 hrs on the clock a season. Every time we board a skier we cut the engine so it gets a lot of starting. The engine is carburatated 408, at 9.6 compression so its not an easy motor to crank. We have a moderate stereo and depth finder in the boat as well.
In the off season I keep 4 batteries, One starting for the ski boat, One starting and two deep cycle for the fishing boat in the basement off the floor and top off the charge every two months. I set a calendar reminder and I can get it done in a day switching between batteries every few hours. I get 5 years or so from the starting batteries. Thats $20 a year for a starting battery, not bad.
If I was on a big lake or the ocean I would definitely have a second isolated starting battery in a boat.
I use Deka AGMs, An intimidator cranking battery 775 CCA for my 115 two stroke and two intimidator deep cycle 900 MCA AGMs for trolling motor. They are clean and recharge fast. I charge once a day while staying at my place close to the lake and generally the deep cycles charge up within 3 hours. AGMs are also known to hold a charge for a long time when not being used. I get around 10 years of use.
If I were to go on an extended campout without any electricity available for two weeks or more at Lake Powell, which I used to do, I would get some large 6 volt Trojan golf cart batteries for my trolling motor which last a long long time. I realize that four 6 volt monsters for 24 v would sink some boats but they will go for a month! Recharging them after a trip like that will take 16-20 hrs or more.
I ran three batteries in my flats boat. Two for the electronics and trolling motor and on starting battery. I ran gel batteries. Wasn't no pull starting my motor so I never spared any expense on my batteries. I always figured they go me around and home. I had a few guys I fished with before I got my skiff and they was always having battery issues. If I thought I had a battery going bad I replaced it. Seven years with that skiff and never had to get a jump or tow. I did use it dang near every weekend so I think that helps. If I recall I replaced the OEM batteries after about a year and a half and replaced the gels once about a year before I sold that boat.
Get the $100 battery and some kind of trickle charger/battery minder. I use a battery tender junior on my boat with a Duracell brand battery from Sam's. When the boat is not on the water keep the battery minder on it all the time, 24-7 365. Batteries will last a very long time.
For redundancy you could spend another $100 or so and get one of those lithium jump starters. They take up little room in a small boat.
Back in the day we would let the boat's battery sit and throw a regular battery charger on it the night before a trip. Batteries would only last a couple of years that way. I got better than 10 years out of my last boat battery that had a battery tender on it.
Best advice I have here is listen to Hawkl. From what I've read here he knows his shiet.
All I will say is that with what I've dealt with the last 10 years as far as boat batteries is take them in in the fall and put them on a trickle charger and check the water (distilled) in the spring when you take them out. I am currently running a sealed and an unsealed battery I bought with the boat 5 years ago and they both hold a charge well. Buy decent and take care of them and they'll be good to you from what I've seen.
Thank you.
And here I thought all those years in the business was a waste!
Anyone with a hydrometer can verify state of charge or test how in-accurate their automatic charger is (EZ RED makes a nice, simple one). A battery reading 1275-1300 is good for three months if away from heat above 70 degrees and direct sun and won't freeze above -15 nor sulfate internally.
If its a wet battery and its sealed, it will need monitored with a voltmeter or charger by OCV readings away from surface charge.
Newb boater here. And despite my profession, I'm a minimal maintenance guy on recreational stuff.
Are you saying that batteries shouldn't be kept in summer temps over 70 degrees? Common here to not see night time temps below 70 in summer.
Sulfate internally???
Surface charge????
Wet batteries will discharge quicker as temperatures go up during storage. As batteries discharge, the plate paste oxidizes. If left discharged the paste oxidation can create enough of a barrier that the chemical reaction from charging cannot take place. In bad cases, it can ruin the battery.
Four mainly starting a 115HP 4 stroke, what is the difference between a $100 battery and a $400 battery? This is a recreational boat, with a battery charger installed on boat. Boat also has a 9.8 kicker that has its own fuel line to main tank. It’s a pull start. One Garmin fish finder, and stereo.
Side bonus question:
Wouldn’t doubling up on two $100 batteries with a switch be better than one of the $400 batteries?
Yes... IMHO.....yes. It's exactly what I have done on our camper..
Quote
And the double or nothing side bonus question:
What battery do you recommend for the above application?
Only thing I will say is to stay AWAY from the X-2 AGM batteries - site here: https://x2powerbattery.com/ (at about $340 ea) because they will NOT hold a charge.. I've tried three (first two replaced under warranty within the first year each) and the latest one - even with a battery tender on it - failed to hold a charge.. I dropped that POS off at the local auto parts store and bought one of them no-maintenance standard battery (series 31) and saved another $200+ overall. That third battery the original store would not honor any coverage on it.. Lesson learned.
If that's all you plan on running on your boat you answered your own question. Two $100 MARINE batteries linked together through a battery selecter switch will last you three or four years if you maintain them during the winter. I ran the same setup on my boat. The engine, fish graph, autopilot, radar, temp probe, fm radio, down riggers, washdown pump and interior lights were on the main battey. Safety stuff (VHF radio & gps/chart plotter) were hooked up to the spare (isolated) battery. YMMV...
Lithium...They're getting very popular but they have a real problem if you charge them below 32F. Charging them when cold can do permanent damage to them. There's new tech that allows some to be charged when cold but I don't know how widespread it is now or whether most automotive batteries have it now.
As long as you don't run really long hard days or all weekend without charging you will be fine with one group 24 or better yet a group 27 marine cranking battery of whatever your budget allows. If you are going to run harder, longer, or add more electronics you may consider adding another battery, a deep cycle would be ideal. Unless you have a boatload of cash, I would avoid all the AGM and gel cell hype and just get a flooded lead acid type for around $100 bucks.
I run a group 24 starting battery for the motor, hooked up with an isolator is a group 27 dual purpose. 24 is isolated to start the motor only. 27 is to run electronics live well etc. That way if I spend a lot of time without running the motor it will still start.
Two yellow top group 31 optimas for trolling motor use only. Spendy but 16 + years old and going strong. Only run a charger when needed, never leave it hooked up otherwise, can overcharge cause problems.
I wouldn't over think this. I use a 29 starting battery on my motor and electronics, and have two 27' deep cycles for the trolling motor. 27's are all that fit in the battery compartment. The whole works is tied into a three bank automatic charger and when the boat goes in the shed, the cord is plugged in. All day, all week, all winter. Let the charger do its job.
When the batteries die, they die and you get new ones.
It would be wise to have a matched pair of dual-purpose batteries linked by a (make-before-break) battery switch so you can reserve a fresh start battery that will not be drawn down by accessories, while being easy to combine them for charging off the main engine. There is no need to spend $400/battery. Flooded batteries provide the best bang for the buck.
No battery expert. But I’ve tried to stay away from lead- acid batteries in boats. Most battery failure is caused from cells shorting together. Caused by segment in bottom of battery. Vibration and pounding of a boat increases this. Hasbeen
I like your set-up, and I'm personally geared towards redundancy on any critical system.
Question... Could that battery selector switch, or something similar be used to connect to a trolling motor battery for an emergency start. Would doing so complicate the charging system? Also, would the 1&2 switch position work with different style batteries? (deep cycle and starting)
I don't think it would work well for connecting the trolling motor battery in the situation you mention because the positive cables attach to the switch. To have the trolling motor battery backup you'd have to figure out a way to ground the trolling motor battery to the engine also. Mine are isolated from the boat's electrical system and I prefer that. I carry a tool kit on my boat, my plan if both starting batteries fail is to simply unhook the trolling motor batteries and swap one into starting battery's place. I've never had to do it but a minute with a 1/2" wrench will have the batteries swapped. I figure if I can't get it started with four batteries then I've got something else that's the problem.
The switch should work fine with different style batteries, it's just a basic isolation switch, nothing fancy. Those switches are the norm on smaller saltwater boats with two battery setups. Something used offshore needs a bit more redundancy than your average bass boat.
Four mainly starting a 115HP 4 stroke, what is the difference between a $100 battery and a $400 battery? This is a recreational boat, with a battery charger installed on boat. Boat also has a 9.8 kicker that has its own fuel line to main tank. It’s a pull start. One Garmin fish finder, and stereo.
The cheaper batteries have conventional, wet-cell construction. The more expensive batteries are typically AGM batteries, which are sealed and immobilize the acid in a fiberglass "sponge" to prevent spilling and leaking. AGM batteries are ideal for motorcycles, ATVs, and snowmobiles, where there is lots of vibration and the increased possibility of unusual positions (like rolling upside down). They are great in the marine application, as well, but I (personally) haven't found them worth the extra cost.
Originally Posted by RAS
Side bonus question:
Wouldn’t doubling up on two $100 batteries with a switch be better than one of the $400 batteries?
In my opinion, yes.
Originally Posted by RAS
And the double or nothing side bonus question:
What battery do you recommend for the above application?
I like the group 27 deep cycle batteries from Costco or Sam's Club. More info listed below:
My first boat had a single Yamaha F115, and I had a two-battery setup - one starting battery and one house battery for everything else. Instead of a 1-2-ALL battery switch, which I avoid, I had a 65A Blue Sea Add-a-Battery setup. The automatic charging relay is no-hassle way to go - just turn the battery switch on at the beginning of the trip, and turn it off at the end of the trip. Easy!
The charging relay makes sure both batteries charge, when the engine is running, and both batteries are isolated when the engine is off. You can run the house battery completely dead, and still have a fresh starting battery to get you home.
If your 115 outboard puts out more than 65A for charging, Blue Sea makes a 120A version, as well.
My current boat has twin outboards, and I run a 3-battery setup - one starting battery for each outboard and a single house battery. I use group 27 deep cycle batteries from Costco or Sam's Club. They have a high enough MCA rating to use as a starting battery, and they have enough storage capacity to function as a house battery. For $82 they are a bargain! I just replaced my two starting batteries for this season; had the old ones since 2016. They still worked fine, just replaced them as a preventative maintenance item. I replace my trailer bearings before they need it, as well. I figure I'd rather change them in my driveway than along the side of the road somewhere, with minimal tools and traffic whizzing by.
My Mercury 2010 115 hp four stroke came with one group 24 battery when my boat was new. Near the end of the season if I didn’t keep the battery charged cold starts became iffy.
I changed to a dual battery system with group 27 batteries and cold starting issues later in the season went away. Keep the terminals clean and connections tight and minimal problems.
3rd boat thread I've stayed away from in the past couple of weeks, even though I've made my living in the marine industry for the last 31 years. I learn so much here. 😁😁
