If I have a two bank charger, can I run one bank to the starting battery and the other bank to 2 or 3 batteries that are wired together in parallel 12v?

No. Each battery has to be connected to its own charging bank.

The charger will see it as two 12V banks, but you will probably get uneven charging with the different charging rates and characteristics of the two banks. Bottom line is yes, it will work.

I would hook up the two bank charger to your two trolling motor batteries and then charge your starting battery every once in a while with a portable charger.

A 3 bank charger would be the proper thing to have for your set up.




https://www.minnkotamotors.com/Support/F...-charger-bank-/

Here's what I have. 4 batteries and a 12v system. But three batteries are wired 12v for trolling motor. And then there's a starting battery. Just bought the boat like this. I don't want to buy a 4 bank charger. The pro mariner dedicates Amos where needed so I thought that may be the way to go. So when starting battery is charged, then the amps will be dedicated to charging the 12v "bank" of three batteries wired together. They are all the same exact battery.

Will this work?

The problem with the 3 batteries in parallel is that they will eventually become uneven and charge at different rates, also if one goes bad it takes out the others. It also takes way longer to bring them all up to full charge.

I have used an automatic charge relay system on my boat for over 12 years; 2 bank charger with 1 12v starting battery and 2 12v deep cycle trolling batteries combined for 24v motor. The 2 charger banks are hooked to the auto relay along with the charging lead from the outboard, the relay has leads to each battery individually. The relay varies the charging from the outboard or the 2 bank charger to each battery as needed. When it senses a 24v load it combines the 2 deep cycle batteries for 24v. It can also be wired to control charging from the tow vehicle. Have had no problems at all and it is nice to have the outboard topping off the batteries as needed when cruising.

Don't remember the name of mine but a quick search shows there are several on the market now.

It is recommended to have a independent charge on each battery. Each battery is a bank so if you have four batteries you will need a four bank charger. You are only stressing the charger and batteries doing it the way you are wanting to do it.

If the batteries is in parallel, what you are wanting to do is the best way to charge the batteries. If you try to use a multi bank charger on paralleled batteries, the charger could read itself on the other batteries, "think" it is charged and go into a reduced charging mode or cut off. Just be aware that whatever amp charger you have is going to determine the length of time it takes to charge.
John

This is what I was thinking.

I didnt know that using separate banks on one 12v big bank would work.