Lithium and lead acid together sort of

waltv

New Member
I have a boat with 2 batteries. One for the trolling motor battery in the bow. Another battery in the transom area to start the outboard motor.
I would like to use a lithium battery for the trolling motor. The owners manual shows the 2 negative terminals for each battery joined together and connected up to a common ground. The positive terminals are not joined together. the positive on the bow battery supplies power to the electric trolling motor, the positive on the transom battery supplies power to run the electronics and start the outboard motor.
Question: I would like to use a lithium battery for my trolling motor. Can I safely do this under the above senario, when the transom battery motor is a lead acid battery?
 

Bob B

Photon Sorcerer
That shouldn't be a problem. Sometimes they connect the negative side of the batteries together to reduce trolling motor interference ... If you have interference .... you could try to isolate them.
 

BroomJM

New Member
That sounds like an exceedingly complex system that would only be necessary if your batteries were mounted close together. I would just ground the aft battery separately. When you install the battery in the bow, for the trolling motor, I wouldn't bother connecting it to the same ground as the aft battery.

Just out of curiosity, your trolling motor runs on 12v or 24v? I'm guessing 12v, but you have me wondering is something is wired wrong.
 

waltv

New Member
That sounds like an exceedingly complex system that would only be necessary if your batteries were mounted close together. I would just ground the aft battery separately. When you install the battery in the bow, for the trolling motor, I wouldn't bother connecting it to the same ground as the aft battery.

Just out of curiosity, your trolling motor runs on 12v or 24v? I'm guessing 12v, but you have me wondering is something is wired wrong.
thanks for your reply BroomJM. Nothing is wrong as I have not wired it yet. the trolling motor, which is a Motor Guide, is 12v. I'm just going by the Motor Guide Manual that came with the trolling motor, which shows the 2 negatives joined together, the aft and the bow batteries. I'm guessing it's to eliminate interference as Bob suggests.
 

BroomJM

New Member
thanks for your reply BroomJM. Nothing is wrong as I have not wired it yet. the trolling motor, which is a Motor Guide, is 12v. I'm just going by the Motor Guide Manual that came with the trolling motor, which shows the 2 negatives joined together, the aft and the bow batteries. I'm guessing it's to eliminate interference as Bob suggests.

OK, in that case, you don't have to worry about running both batteries to the same ground. I've been running a bass or fishing boat for close to 30 years and if your two batteries are at opposite ends of the boat, you don't need to go to that extra effort...it's only if they're sitting right next to each other, in the stern. That's how some boats are configured, to keep weight out of the bow. Just run your front lithium battery for the trolling motor and everything else off the cranking battery.
 
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