So I have a 3 year old RV. I bought it used from dealer. They put in a new deep cycle battery. So I usually have the camper connected to the house AC. Last fall I tried to activate the slide out motor and got nothing. Wound up the battery was dead so I put it on deep cycle mode of my car charger. Charged up, and slider worked.
So it is, and has been on AC. I tried the slider and it is dead. Measured battery, zero VDC. So I have it on the car charger again.
I never had a camper, and I hate this one (wife idea). So LEDs work inside on AC, but battery does not get topped off by AC. I guessed it would have a trickle charger, or you just have to chage the 12V all the time? That seems silly, but again I dont know. I think this thing is just a PIA.

You should have an inverter charger built into the RV that charges the battery when plugged into shore power. It is good practice to disconnect your battery when storing the RV, as lots of things have parasitic drain on the battery. Draining a new battery down to zero will kill it dead. If you are saying a known good battery isn’t being charged by your inverter when plugged into shore power then you either have a bad inverter or a bad connection.

Thanks, that what I thought. I imagine it had a bad inverter / connection when I bought it. Hence the new battery.
I had my knee replaced a month ago, so dicking around with it is hard to do right now.
Hope the dead battery takes a charge.

Well i got the battery to charge to 13.8 VDC.

Had the RV disconnected from AC, but the battery fully charged and connected. I had zero power inside the RV. No lights, no fans, no slider.

Plugged the RV into AC and the lights fans and slider now work.
So my guess is the battery is disconnected from the lighter loads, but somehow a relay kicks in the battery to
drive the slide out motor. Makes sense because with a dead battery, the slider is dead. AC alone wont activate it.

RV dealer is huge, but they seem to be weasels. I will try to fix it myself when I can walk again. I don't want to take it there. At least I got the slider out so we can clean it out for the season. I guess in a pinch I could use jumper cables if the battery dies. I can take a trickle charger on trips. Half a$$ed repair, but I got other stuff for the moment to do.

Have you cleaned all the cable connectors? They grow some great stuff between the surfaces while sitting dormant.

If the new battery has been fully drained, its likely damaged. It might charge up over 13v but it won't hold it.

Take the battery to an auto parts store for a free load test.

Also check fuses and circuit breakers.

Thanks for the help guys. It is good to have ideas because right now I am crippled up with a knee replacement, so everything takes longer to do. If I work too much my knee swells and I can't do good PT, so I have to limit my projects unfortunately.
I'll have my wife cycle the slide out while I measure the battery as a load test.
Battery has 4 posts, 2 male standard posts, and two threaded screws. Amazingly clean connectors, no corrosion. It is using the threaded screws for the single +, - lines. Made in 2019.

I think fuses are that stuff is under the bed. I have the manuals, so I can look it up.

My big thing was to see the motor was not fried for the slide out. At least I know where to look now.
I can picture wires not connected, or a fuse, or a bad relay.
Seems like battery is isolated except when driving the slide out. Worst case if I am out camping I can get the slider to work via jumpers and my truck.

Again thanks. Ter

A 12V deep cycle is considered fully charged at about 12.6V and fully discharged at about 12V. That's about 50% of it's total charge and you don't want to go any lower.

Deep cycles will have a Reserve Capacity rating. It the number of minutes it takes for a fully charged battery to drop to 10.5V under a load of 25 amps. It can be converted to amp hours/minutes/seconds with some math but it's any easy comparison of batteries as it is. For example, using 6v batteries that are commonly used in RV's, a Costco 6V golf cart battery (made by Interstate) will have an RC of a little over 100. An Interstate green top will be more than 400. It'll cost 50% more than the Costco but will last 4x longer. RC applies to all deep cycles, not just 6V.

Very cool, I appreciate the knowledge.

Campers can make you scratch your head and swear a lot, at least mine does. I have been having the same issue for 2 years, I shut almost all power to the inside and It will still kill the battery in about 3 days. The almost all power is the small light that is on a co detector that I can't figure out how to shut it off, probably for safety ya can't. The main breaker doesn't even shut it off, only time the light is out is when the battery is disconnected. Not even a way I found to remove the bulb.

Although not a RV,mine is pop up slide in camper. My battery power is two 850CCA truck batteries. If I do not disconnect the batteries from the camper, they will not charge all the way.I have 800W, 2 cycle Harbor Freight Generator that I can plug the battery charger into, or run the camper directly off the 120V that the generator supplies, but the camper inverter changes it to 12V

Check the fluid level in the battery.

I'll bet it's dry....

I've been out of the industry for a while, but it used to be with RV's and motorcoaches plugged into power=charging, generator running=charging, going down the highway=charging, whether it needs it or not. If the manufacturer says it automatically shuts off, they probably have no clue or are FOS. Many do not shut off and worse, charge at voltage levels 12 v deep cycles don't respond well to.

The lower charge voltage that 12v deep cycles need are usually exceeded by all three of the charging applications found with RV systems so they overheat, lose water and the charging exacerbates the problem until there is no liquid left and the only time they work is briefly after they have a charge applied to them or connected directly to power, similar to what you are experiencing.

If the water level is gone, fill with distilled water to just cover the plates and charge with a 2 amp MANUAL charger for up to 48hrs MAX, check specific gravity with a hydrometer and cross your fingers....
Cease plugging to power when stationary; they will set stationary easily for two months with no load on a full charge (hydrometer verified); then disconnect the battery.

RV's basically run juice through the battery instead of allowing a battery to store energy, run items, then recover again, like they are designed to do. Energy exerted beyond the storage ability of the battery turns to heat which removes liquid from the battery; as liquid gets less, so does the capacity of the battery since the liquid is the vehicle that plate material is activated and releases energy through. Anything not submerged is surface area not capable of taking a charge or releasing stored energy .
With AGM batteries this can even damage them to where they won't recover at all. With wet batteries, if the heat hasn't burned off the paste, they can recover by adding distilled water back and manually charging until specific gravity shows a full charge with all cells within 20 points.

I had same problem and found some campers have an in line fuse/circuit breaker to the battery from the inverter. cost about 6 bucks and mine was bad. Just follow the hot wire from the inverter to the battery you will see a device about 1 or 2 inches in size. I am betting that is bad.

Is it in-line fuse you're talking about?

It is an inline fuse/breaker mounted on the chassis between the inverter and the battery

It solved my problem, a little breaker mounted to the frame had 1 post rusted off. Been chasing the issue for at least 2 years and fixed it for $5 and about 1/2 hour time. Thank ya very much.

5 years ago I bought two size 34 12 volt Marine/deep cycle Duracel AGM batteries for my camper from Sam's Club for $119.00 each....I just replaced them with two identical batteries from Sam's Club for the same price.

I price checked several other places and the same batteries were going for $200 and up .