I've got 2 battery banks to maintain. One of them has a 50A victron charger on it and all winter I'll leave the camper plugged in so I shouldn't have to worry about parasitic discharge. I have shunts on the battery banks and apparently those draw 12ma.
On my second bank, however, presently I have nothing to keep it charged. I do own a watt cycle charger, I think 60A model, but, I'd like to stick a 5A onboard lithium charger in to just keep that battery from discharging too far. Is that a bad idea? Would a larger charger be better?
Or, perhaps rather than have either one of the 2 battery banks actively charging, I should disconnect them and let them discharge to 60% for the off season? Is there a charger that would be appropriate to use that would keep them only partially charged like that?
My understanding is that they don't lose much charge if they are disconnected. So my inclination would be to charge them to 60% and call it done.
The note on my shunt says the 12ma current can drain some batteries in a bit over a month. A while back I built some battery monitors running on a shelly Uni. With some smart home integration from active monitoring, I should be able to kill power to the battery charger when it gets to some high level capacity, and then turn it on when it gets down to some minimum voltage. I just don't want to let it drain all the way down to the point of damage.
What would have been perfect is if the Watt Cycle app had a "Storage Mode" setting you could set the batteries to, and it would just maintain a 60%-ish level indefinitely.
@Tim I did some math. 12ma for 24 hours is 288mah. So in 30 days, the draw would be 8.64 amp hours. If your battery is a 100ah battery, that would reduce the charge by 8.64% each month. So it would go from 100% to 0 in a year. That seems to mean that storage for a couple months is ok but much longer is a problem. Right? And of course a bigger battery would drain more slowly.
If you need to leave the battery unattended for several months one option would be to get a cheap trickle charger and put it on a timer to charge 15 minutes a day.
