Batteries once again.

[Pagetslady]

I have two 12volt batteries connected together to give 12 volts have had the charger on today came back on board to find one battery very hot I have turned off the charger and have checked the specific gravity and all bar one cell are around 75% charged the odd one out is 100% charged, is the over heating battery faulty, the voltage was 13.6 just before I turned off the charger.
Mike

 

[Dave_Seager]

It sounds as though the odd cell has failed which means you must replace that battery.

The same thing happened to me this spring. I put an automatic charger on. After a while all the cells were gassing freely although the charger did not think the batteries were fully charged. I disconnected the charger and let the batteries stand for a couple of hours before testing with a hydrometer. When I came to check the batteries the cells in one battery were still gassing. When I tested the cells they all showed a good charge except one.

What was happening was that the battery with one cell failed was giving about 10 volts and the good battery 12 volts. When they were connected together, the good battery was charging the five good cells of the battery, causing it to get warm and to gas.

 

[VicS]

I have two 12volt batteries connected together to give 12 volts have had the charger on today came back on board to find one battery very hot I have turned off the charger and have checked the specific gravity and all bar one cell are around 75% charged the odd one out is 100% charged, is the over heating battery faulty, the voltage was 13.6 just before I turned off the charger.
Mike

Odd.
Are you sure about one cell being fully charged... not completely discharged by any chance?

 

[William_H]

Batteries in parallel

This is an example of what can happen with batteries in parallel when one goes bad. The solution is firstly to separate the batteries and treat them individually. ie charge then check voltage and test for engine start and life running lights. I think you will find that the bad battery will become obvious and you will have to discard it. The other may be quite oK. I would not put so much store in results of SG (hydrometer) test but it may in this case show the bad battery cell. good luck olewill