Batteries fine 1 day, drained the next

[jxm99]

Picked up the boat from the yard where she was getting her bottom painted. Batteries were off for the week, not plugged into shorepower. Fired her up fine, took her out for a cruise and returned home. Followed the usual procedures of shutting her down and connecting to shore power.

Went to the marina yesterday, port engine came on with a little coaxing but the starboard didn't want to go. Checked the battery power gauge and it showed around 8V. Tried to get the batteries charged up with one on and bridge over to start the starboard. Managed to get the starboard started but the low battery alarm came on pretty quick and that was the end of boating for that day. never even left the slip!

The boat was hooked up to shore power and was taking electric as all system were running fine from the shore power. Any thoughts on what this may be?

Thanks

 

[HUMPH]

Bad alternator it sounds like to me. Same thing happened in my 320.

 

[chandalen]

A battery can be so dead that its just a drain on the system. Replace it completely with a known good battery and try again. Also alternator can be checked WITH A CAR not sure how wise this is on a boat... while its running remove the neg. terminal from the battery. If engine still runs the alternator works (at least to give the engine power)

 

[Bt Doctur]

Only if you want to blow the alt too and maybe every piece of electronics and 12 bulb system on the boat., you NEVER remove a battery cable with the engine running.
you check voltage with a meter.