Expert: tyler boehner - 3/14/2008

Question
I have a dual battery system, with a bait pump battery wired in.  A professional wired in an isolator and a marine charger several years ago.  Due to some heart surgeries I've not been a good boat owner for the last three years and the batteries have gone dry a couple of times with the charger plugged in.  I'm gettiing to retirement and am trying to get the boat back up to fishing speed.  I put in Costco heavy duty batteries less than two years ago, but I've allowed the batteries to go unattended and dry up.  Two days ago I filled them yet again and left the charger to do its job.  Overnight the batteries were sufficiently charged to fire up in the morning and start the boat without a problem.  I cruised for about two hours. I had both the radar and the GPS on.  The ampmeter started a about 14 V, but dropped about a half V when I turned the electronics on.  At the end of two hours after I docked, I tried starting the engine again and the batteries are dead.  Do I have a recharging problem with a weak alternator or did I simply kill two inexpensive batteries with neglect?

Answer
I am not a battery expert but if the motor was running at 14 volts than i can tell you that the charging system is working as it should.  The batteries are probably shot.  I would also check out your charger.  If your charger is overloading your batteries so much as to dry them up, it is overcharging.  If you are trying to sell the boat, I would sell as is and warn the buyer that he probably needs some new batteries and possibly a new charger depending on how the new charger acts with some new batteries.  With a battery isolator you shouldn't really need much of a charger if you use the boat very often.  The motor will charge the batteries itself.