I'm going to be getting an onboard charger but not sure what size is needed. I have 2 batteries. 1 is for the trolling motor and one is for the engine. Not sure if more info is needed to determine what size charger is needed.
It depends on how fast you want your battery to charge up between outings. If you have a 80AH battery and you want to use it in 2 days from now, a 5A charger is probably fine.
Six to 10 amps per bank will be sufficient unless you fish all day and deeply discharge the trolling motor battery. The problem with say a dual output 20A charger is that the engine start battery rarely needs that kind of charge rate and those chargers can be spendy. I use a 6 amp single bank for the troller and 1.5 amp Schumacher maintainer for the start battery. Works just fine. I fish all day and about an hour after dark. I've never had the 6A charger fail to keep up. A 10A would be sufficient for your use. Even a 100Ah battery thats deeply discharged would be fully charged overnight.
