used a 35 mm SLR with watch batteries for 35 years ,just change battery once a year good to go no matter how long camera set.now have a Canon Rebel and a couple point and shoot ,it a pain to remember to charge them up every month or so when i dont use them,and the batteries go dead ,will it kill the batteries to where you have to get new ones if I just let them just discharge till they are dead and set around ,and recharge them when i need it for a trip?I know it use to be hard on cell phone and car batteries if you did this

I would guess the watch batteries in your old 35mm slr were for maintaining the date/time. Minimal drain. The Rebel line has gone from NiMH which need to be recharged even if sitting unused to Lithium which has a long standby life. As a practice, I pull the batteries out no matter the type from DSLR's and only insert them day of shooting. Point and Shoots are largely Lithium but I apply the same procedures because the last thing I need is to grab a shot and find that it won't power on because the battery is dead.

thank you , will try to keep charged and out of camera ,did not think of that one ,..my old SLR's were so old(about 40 years old) ,they did not have date and time ,watch battery (flat round disc battery) only ran the shutter ,and red and green light to let you know the F-stop was set right ,.batteries lasted a very long time ,

I charge the primary battery and any extras that I am taking along the night before going out on a shoot.