I have a second battery for the van and have occasionally run it flat by

using it to power the fridge for several hours with engine off. When I
restart the van the battery recharges from the alternator. But it
DOESN'T blow the 15A fuse in the charging circuit. AFAIK there's no
current limiting system in the alternator/rectifier, and the alternator
hasn't fried,
so the internal resistance of the battery must be limiting the charging
current.

What is the charging current for the battery? What is it's internal
resistance during charging? Does it vary as the charge increases? How
can I work out how long it takes to recharge the battery?

Incidentally, this battery was sold to me as a "deep cycle and starting
battery", and is manufactured by BHX (here in the UK). It's a big
bugger, so reading Joel's post I presume it has numerous thick plates
inside.  Rated at 120AH, I forget the CCA.

The more I learn about these things the less I seem to know.

JP Nicholls  /  jpnicholls@lucent.com