12 volt power and stereo power up and down

[st68]

So I am trying to figure out what the problem is with my boat. When I go to fill my ballast sacs sometimes the pumps work really weak... at the same time the stereo will be on faint or not work at all... other times everything will work just fine. I always with boat turned off... when this happens I try to turn key to left and then to right but it doesn't help. I also try with engine running idle but this doesn't help either. This weekend it was happening again where the pumps were weak and the stereo was weak too... I put the boat in gear then everything started working normal again... put back in idle with engine running to get the job done... after we were done surfing I turned the engine off and used the pumps... they were working normal again. I am wondering if this is a battery issue, alternator issue??? Thoughts? Thanks.

[Bruizza]

Sounds like a battery issue to me. I would start by putting the battery on a charger or pulling it and having it tested at an auto parts store.

[chpthril]

Sounds like the house battery has give up the ghost and no longer holding a full charge. if so, I would consider replacing both due to age.