Cooking batteries

John and Anne on Bali Hai <annejohn@...>

I recently had a problem caused by a defective solenoid which meant
that the engine could not be started. Initially I suspected that the
12 volt starting battery had failed. I called in a mechanic who
replaced the solenoid and tested the batteries using a sophisticated
load tester which proved that the starter battery was fine but that
one of the house batteries was dying. It was one which I had suspected
as I had put a voltmeter on each battery after they had been on charge
for some time in a marina. There are four pairs of 105 AH 12 volt
batteries on my boat and they are all nearly six years old. The meter
gave a reading of 13.4/13.6 on six of the batteries but on the other
pair the reading was about 14 volts on one and 12.2 on the other. It
was the latter one that failed the
load tester and it was replaced by the engine battery and I fitted a
new starter battery.
Now that I have removed the protective film from the condition
indicators on the batteries I can see that three pairs show green and
one pair shows red. According to the key on the new battery there are
four stages, green when new then black then red and finally white when
the battery is dead.
The total capacity is 4 X 105AH = 420AH when the batteries are in good
condition. The experts advice is that means that there is 105AH to use
before it is necessary to recharge then. This means that charging
should start before the reading on the E meter shows more than 25%
discharge. Exceeding that figure will progressively speed up the death
of the batteries. In practice this means that there is only about 15%
of the nominal capacity available for use each day as it is
uneconomical to keep the generator running when the batteries are 90%
full as the charge rate is so low.
Finally, Christmas is coming and if you do not already have it I
highly recommend Boatowners Mechanical and Electrical Manual by Nigel
Calder. It is expensive but worth it's weight in gold so put it on
your wish list.

Best wishes, John SM 319

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