Battery problems

[Peter]

Some questions on battery problems, on my yacht got 3x 110AH house batteries, all "standard" leisure batteries, plus engine start. None of the batteries are holding charge (one house battery has green indicator showing its OK), all reading approx 11.5 V. Only problem was a couple weeks ago the battery charger had a funny turn (its enclosure gets hot, now resolved) and was putting out approx 14V plus, then the alternator went pear shape, before going pear shape putting out high voltage, then stopped producing charge. At present charger is OK and after a days charging batteries still not holding charge, and changed alternator. My questions are:
The batteries have low electrolyte level, if I refill with distilled water will they be OK
Is there any way of testing a battery to see if it OK of knackered.
Have I cooked the batteries and are they knackered
What devices area on the market to protect batteries from overcharging/over voltage.

Thanks

Peter


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[Robin]

IMO your batteries are DEAD, a fully charged 12v battery will show 12.8v, 11.5 volts is less than flat. !4v plus at the alternator or charger by the way is quite normal, 14.2 - 14.4v is OK on charge and 13.2-13.6v perhaps when charged but still connected. How old are the batteries and have they been regularly drained maybe by a fridge to below 50% (12.2v say)?

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[tritonofnor]

Refilling with electrolyte (distilled water) may help for a while, but if the batteries have been cooked then the chances of recovery are slim. The only way to test reliably is to give them an overnight charge, disconnect them and then put a discharge tester (which puts a heavy load across them) on to each in turn and see if they hold voltage. My local chandler/engineer is always happy to lend me his tester if he thinks he's going to sell me a new battery!

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[claudio]

It sounds like you've got shorted cells in your batteries. You could try topping up with distilled water, then recharge. Test electrolyte with a hydrometer. If there is a significant difference between the cells, the battery needs to be replaced.



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[silverseal]

If your alternator is damaged, but still connected to the battery source, you may have damaged "blocking diodes" which stop reverse current drain from the batteries to the alternator. Measure the voltage of the batteries, then disconnect them from the wiring loom - if the voltage increases after an hour or two, then the alternator needs checking to check out the blocking diode(s) some times there are two

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