I recently purchased a bass boat, everything worked fine when test drove, but the first day I took it out on the water the TM didn't work. After testing the batteries with a voltmeter all the batteries were fine except one that read as negative 11.9. I have a mini kotA I-pilot and there is still some power coming to it as when I click the test battery button on the motor it will light up but it will not turn on or sync to the remote.  I am new to boats and deep cycle batteries does anyone have some advice? 

50 minutes ago, Kyle Walker said:

I recently purchased a bass boat

From where? New or used?  Warranty or As-Is?

Where did you take the measurement from with the multimeter?  If you got a negative reading, that means it was connected to the battery backwards.  If you did that at the battery terminal, are you sure you had the right wires from the multimeter on the right terminals?  Also, 11.9 is low and definitely not a fully charged battery.  Did you charge the batteries before you tried it?  What did the other battery measure (if 24 V)?

Are you sure you did not connect the meter leads backwards?  The only time I've ever seen a battery have reverse polarity is when it was almost fully discharged and the charger was connected to backwards and charged backwards.  I've seen this a few times but I have never seen a battery just reverse polarity on its own.  I assume it has a multibank on-board charger so I don't see that happening unless someone connected the charging cables to that battery backwards and not real sure you could do that with getting some smoke from a fully charged battery. 

In a series connection, I'm not sure how you could get any voltage from them if one is backwards.  Never tried connecting one backwards to see what would happen, and probably not something I would want to try.  It's like sticking multiple batteries in a toy, put one in backwards and the toy does nothing.

meter leads are backwards?  i still do that on occasion.  

Don't just check what colors are connected to what poles of the battery, also check what sockets the probe wires are connected to the multi meter.