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