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In article <BzEqn6.JMv@cck.coventry.ac.uk> lsg001@cck.coventry.ac.uk (Graham Wilson) writes:

>  If you have a bank of 12 volt batteries of 500 amp capacity, what is the 
   highest amp hour charge you can put into the batteries without cooking
   them ?

>  Is there are a formula for working this out ?

I assume they are deep cycle lead acid,
and that you mean 500 amp-hour, not 500 amps.

Let C be the amp-hour rating (500 in your case).
You can charge it at C/20 amps (25 amps in your case) until fully charged,
which will take more than 20 hours.
You can also charge it C/10 amps until 90% charged,
then do the last 10% at C/20 amps.
You have to stop when fully charged (check V or S.G.).
You want to prevent gasing, which damages the battery.

Note that simple automotive chargers do not charge at constant current,
which these methods require. A 20 amp charger will only supply 20 amps
to a dead battery, and gradually decrease to a few amps when fully charged.
Alternators with a voltage regular are similar,
although a 50 alternator does not charge at 50 amps!

I read this in "The Complete Battery Book".