Marine battery charge slowly drops

[WhereBob]

I have a delco marine battery that takes a charge to around 13 volts. Over the course of a few days that charge has dropped to 11.5 volts(It had sat all winter without a charge). Normal? Should I recharge it again? Should it hold at 12.5 + or do they discharge continuously over time?<br /><br />Thanks<br />Bob<br /><br />PS this battery is used for starting the motor and running a fish locator.

 

[Paul Moir]

Re: Marine battery charge slowly drops

They do self-discharge, but I would expect mabey a 20% drop over the winter and you have what appears to be a 100% drop. They should stay at above 12.2v for over a year (at room tempurature).<br />Of course, all voltage measurments are very dependant on the tempurature of the battery.<br />Are you using an automatic charger? Is is set for the correct mode? Are you sure the battery was fully charged when you put it away?<br />Recharge it and have it load tested.

 

[Boatist]

Re: Marine battery charge slowly drops

WhereBob<br />All lead acid batteries self discharge and should be charged at least once a month. The battery voltage should be 12.6 volts at 70 degrees.<br /><br />To start with are you useing a good digital volt meter or the one on the dash. When charging your battery should reach at least 13.8 volts and current drop to less than one amp. Some Automatic charger will charge as high as 14.8 volts. If your charger is not reaching at least 13.8 volts then your battery will likely not be fully charged.<br /><br />12 volt batteries have 6 cells of 2.1 volts each so if your meter is good and your charger is good then you likely have a weak or bad cell in the battery. Check the battery water level if it is the type that you can check. After fully charging check the specific Gravity of each cell with a hydrometer. You can get a cheap one at most auto stores or even wallmart. They will show you if you have a bad cell.<br /><br />You could also put some load on it, Lights, Blidge blower, radio for a while and then try and start your boat. You can here engine crank slow with a weak battery.

 

[WhereBob]

Re: Marine battery charge slowly drops

Thanks for the replys guys. I am using a good voltmeter. I think the battery has a bad cell, I charged it again last night with a good charger at a 2amp charge to 13.7v and this morning it was down to 11.9v. Heading out to buy a new battery tomorrow.