Pontoon Boat & Deck Boat Forum

Hi all. I am hoping you can help me out. I have a 16' Tahoe pontoon boat on an urban lake behind my house. The lake is electric only and my boat has a 12 year old Duracraft 67lb thrust motor.

Last week I noticed it was running at about half power. After running around the lake for a few hours I got back to my dock and checked the batteries (it's a 24 volt system running off two 12 volt batteries wired in series.) One of the batteries had a bad cell and was completely dead.

My problem now is I bought a new battery identical to the one that is still good and it still runs about half power even when dialed all the way up. I double checked all my wiring, fuses, and connections and everything is as it should be.

If anyone can help shed some light on this I would greatly appreciate your input.

Best Regards

It could be that you have a good (new) and a so so (old) battery tryingg to work together. Or.......... the motor migt be telling you something (I'm tired).

Measure the voltage at the battery while you have the motor on full. Measure each battery separately.

Check the batteries "Under Load".

If you had a bad cell in one battery, the 2nd might not be holding up under a load.

Yes very often when you have one bad battery it will kill the other.

Thanks everyone. I'm going to head down to the dock tonight with my notes and test meters. I really appreciate the input!

This afternoon I did a few tests.

First I unplugged shorepower (I have a new ProMariner dual bank charger on-board) Then I tested both battery's at the terminal. They were showing 13.5 volts each. While still tied to the dock I put it in full forward and the voltage dropped .5 volts to 13 volts. So, I cast off and checked it periodically and it stayed at 12.5 volts for almost an hour. The wiring is tight, clean, and short as I can get it because when I first bought the boat six months ago it had way too much lead and was getting major resistance and the motor would shut off at high speed after a few minutes.

So, the wires are good and nothing gets warm, the connections are new and tight. The motor does not get warm at all after sustained cruising at full throttle.

I guess next step will be what papyson advise and check voltage at the motor, under load. I'll post results tomorrow. Thanks again to everyone for your help and support.

Might also test the trolling motor to make sure it's not leaking water into the motor, thus causing issues.