need help buying the "right sized" onboard charger
 

what is the "proper" charging amps (for each bank) to buy? i will be using two series 27 trolling motor batteries for a 82lbs. thrust 24v trolling motor

I have heard 10 amps to each bank is a good size to use and the formula says to use a charger that is at least 10% of the batteries rated amps which in this case is 875 so that would equal a 8.75 amp charger is needed.

i don't know if the formula is overestimating the needs so what im asking is, should I buy the 10 amp per bank chargers or could the smaller and more affordable 5 amp per bank charger do the job?

then there is the price, the 5 amp per bank charger cost around $125 and the 10 amp per bank charger run around $250

so is the 5 amp per bank charger ok to do the job well or would it be undersized and not good enough to fully recharge the batteries overnight to fish 2 days in a row?

the way I will be using this onboard charger is to plug it in to recharge right after a trip then not plug it in again except to do a quick refresh charge the night before I go.

I want to save money if i can but not at the expense of not fully recharge the batteries overnight (12 hours) to be ready for the second days trip.

If you fish back to back days the 5 amp may not fully charge them overnight depending on how long you have to charge them.

I went with a 3 bank charger. This way it fully charges the main battery also.

thanks, i'll go ahead and order the 20 amp 10/10 one then. I was pretty sure that's what I needed but I guess I just wanted reassurance before spending the money.

I don't need a 3 bank because the 2 trolling batteries are up front by themselves so a two bank charger is all I need.

I check the starting battery from time to time but it never needs charging because it is just for starting (Suzuki df40) so it doesn't get drained much and starting such a small motor doesnt take many amps so never needs recharging at home (but I do have another charger in case it ever does), the motor recharges it well enough when I use it and they have lasted 4-5 years that way. suzukis have better charging systems then a lot of other motors too so that helps.