I have now gone through my second optima 31 dual purpose battery in 4 months the last one I got I bought the optima charger to use. I have disconnected my onboard charger to start isolating the problem installed the battery used it twice no problems it has set for two weeks and now it's showing 5 volts. My breaker switches where turned off so the only thing I can think is it could be something in the motor drawing it down or the battery but I'm starting to doubt that. Need some help here!

do you have a GPS on your sonor..some will draw amps even when 'off'

Leave your charger hooked up. I have 5 batteries on my boat and have a charger hooked to each of them all the time unless I am on the water.

I do have a GPS puck but wouldn't that be shut off by the breaker I've never left a charger hooked up before all the time and never had any problems I've never had battery problems like this before I bought optima battery I will be checking wires tomorrow with the meter. Could a bad starter cause this?

Best way to tell is to take the positive lead off the battery and put a meter in between the lead and the battery. With everything off, hook up a meter and measure for amps between the positive lead and the positive terminal or if your meter can't measure DC amps, then just measure for 12vdc between the positive lead and the battery positive terminal. Don't run or start anything when you are doing this.

The starter shouldn't be in the circuit with everything turned off. It isn't likely changing batteries caused the problem. Do you have an automatic bilge pump switch, float? I have had those fail and not been able to hear the pump running in the bilge area. They are usually wired direct to the battery so they will always work.

Had a problem just like yours it was a bad voltage regulator that was drawing down battery. Unplugged motor harness and it quit. Replaced voltage regulator no more problems.
Johnny

What motor did you have with the voltage regulator