Battery Questions

[sundog01]

Went to the boat last weekend and my battery charger died, unknown to me. I thought that the batteries were full charged - however - the next morning both were dead with the charger on. Went and borrowed another battery charger and it took all day to charge 1 battery. Next day the same battery was down to 10 volts. I finally got the motor started and fully charged both batteries according to the volt meter. I realize the volt meter is no indicated of amperage. I then had to leave the boat.

My questions are - could the malfunctioning battery charger kill my batteries?
What would cause a fully charged (supposedly) battery to lose charge overnight, with nothing on and the battery switch off?

The charger is of unknown age and the batteries are 2 years old, deep cycle.

I plan on replacing both batteries and the charger.

Thanks for your help.

[sailingdog]

If the batteries were left partially charged for a significant period of time, the battery plates may have sulfated and died. If the batteries were over charged by any significant amount, they may be dead too. If the batteries were down to 10 volts, they were far past the fully discharged point, where the batteries would have been at about 11.6 volts DC.

Have you checked the water levels in the battery if it is a wet cell battery?