>>The fact that some people find the charging rate supplied by the small
>>system adequate in no way means every one will. The amount of alternator
>>current that flows to the aux battery terminal often needs to be greater
>>than what the battery itself needs even for slow charging.

Another consideration is the maximum charge rate that the battery can
accept without being damaged.  I wired up my aux battery charging circuit
to carry 50 amps, then installed a 33AH sealed deep cycle battery (only
$60 and provides plenty of juice for a weekend camping trip).  Turns out
that the max charging rate this battery can handle without being damaged
is 6 amps according to the manufacturer.  So, I went out of my way to
build a fairly rugged charging system, only to use about 10% of its
capacity.  All well, if my pockets ever get deeper I can upgrade to a
larger battery and already have a good charging circuit built in.

jake