Finally getting a bay boat this week and never had to charge multiple batteries before. It�s got a 24volt trolling motor so two are connected. Just wondering what the preferred method is.
Thanks

A multi circuit on board charger is your best bet. Got mine on eBay.
ProMariner-ProSport-20-Plus-20amp-3-Bank-43021-by-ProMariner

Go with a good reputable 2 bank digital charger. If you would like to add the cranking battery, which I recommend, get a 3 bank. I have had great luck with the Minn Kota digitals, and I know others have have had good luck with other popular brands.

It�s got a cranking also. I�ve always disconnected the battery before charging it. Do you leave everything connected with these chargers?

Yes

I have a separate battery for my electronics and went with the 3 bank. I let the engine charge the cranking battery.
Yes leave everything hooked up.

This probably goes without saying but.... the higher the amp, the less charge time required. Big difference in charge time between a 10 and 20 amp charger.

Just saying....

I have a 3 bank Minn Kota charger with 15 amps per bank. It works great.

Bank charger for sure, I�d get a 3 bank charger. if it�s anything 20� or bigger you�ll likely want a 3rd battery and a 36V motor down the road. Not sure how you boat will be set up but the bigger ones sometimes have two separate cranking batteries in parallel so you might consider a bank charger for the cranking batteries if you have more than 1.

Higher amperage comes with more risk too, a lower amperage charger is gonna be safer and offer much less risk of overcharging and causing a swollen battery or producing toxic gas should there be a charger shutoff malfunction.

Not if it is a �smart charger�. And that is the ONLY kind of battery charger you want. No risk at all to battery. These chargers run on programs that sense what the battery needs and applies it regardless of what the peak amperage the charger is capable of. They also act as maintainers. You leave them hooked up 24/7 when not on the water. Owning a good smart charger is your easiest way to maximum longevity and performance from your battery.

This link is to a great site that has great information on understanding storage batteries, their care, and about battery chargers --

https://batteryuniversity.com

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The Minn Kotas (probably others too) condition the batteries after fully charging. I have 3 batteries and a 3 bank charger. My batteries never need the same amount of charge time. My charger starts slowing down the charge at 75% I believe. Mine is a 10 amp, I believe, numbers are hard to read in my console. 10 or even 5 is fine with me because I rarely discharge my batteries below 50% and normally have time between charges. I also have an alternator charger that diverts charging from the cranking battery to the others. If I make a long run back to the ramp I will sometimes get home with 3 fully charged batteries.

any thing electronic is prone to f up be it smart or not just sayin. but to the op, a 2 or 3 bank charger is what ya want. leave every thing hooked up if its in your shop or garage ya mite unplug the charger after it has charged and plug it back in the nite or day befor ya go fishin, good luck!

10 amps per bank is all you need. I have a 440 minn kota on my 4 batteries ( three trolling and one cranking )and it works like a champ. Most Bass fishermen that do tourneys want the larger amps to speed up the charging process between morning and afternoon plus over night . But if you are an average weekend fisherman like most of us 10 amps will do just fine. IMO

I have 3 of these mounted in my boat, one on each battery.

https://www.amazon.com/dp/B00MYTSEFI/ref=cm_sw_r_other_apa_i_FyOeDbB0RNRBZ

I have them plugged into a 3 way adapter and plug it in after every trip. It will fully charge all three batteries overnight. I plug them in when I come in from fishing and leave it til next time I go out. Sometime the next day and sometimes its 2 months but I never unplug them til i go fishing again and it keeps the batteries fully charged all the time. Been doing it this way for 3 years now on same batteries and no issues so far. When I bought them at Walmart 3 years ago they were only $20 each but looks like they're $32 now. Only 1.5 amps so if you need a quicker charge than overnight, there are probably better options out there. I went with these because I didn't need anything more than an overnight charge and if one goes out I just replace that one for 20 bucks (well looks like 32 bucks now). I've had 2 other 3 bank chargers before these and neither lasted more than 18 months. One was BPS brand and can't remember the other one. I think I paid $150 for one of them and around $200 for the other. I like that I can replace these individually cheaper than buying another 150 to 200 dollar unit.