Larry wrote:
"Mark" wrote in news:1156735487.090872.131750@
74g2000cwt.googlegroups.com:

I'm wondering, would one of these things fully charge a discharged
*big* bank of lead acid batteries, like 500AH capacity?

No harm at all. This charger completely shuts off when the red led comes
on at 14.2V and doesn't come back on again until the cell voltage drops
to around 13.2V. The charge you get is very deep, penetrating the plates
very nicely.

I don't understand. To drive a fully charged 500AH battery bank to
14.2 volts requires a charge current of 1% to 2% of the bank's
capacity, 5 to 10 amps. I suspect the little 1.5 amp charger would
never drive the bank up to 14.2 volts.

It [the battery] will only sulfate when when the lead sulfate in suspension gets saturated enough [that] the ions form crystals that gravity falls out into the bottom.

Sulfation which drops to the bottom of the battery case does not
decrease battery capacity. There's space at the bottom of the battery
for just that reason. The battery's service life is decreased;
ultimately enough crud will drop to the bottom of the battery to short
it out.

Large lead sulfate crystals *which are imbedded in the plates* do
decrease capacity; they act like insulators and remove that portion of
the plate from service. It's sulfated plates, not lead sulfate sittin'
in the bottom of the battery, which reduce capacity.

But that's not my question, which is, would slowly charging an 80%
discharged battery for 20 days (which means the battery would be 40%
or more discharged for 10 days) result in sulfation problems?

If you're charging at an average
current of 1.5A and the loads are averaging 2A, that isn't going to work
and you'll arrive at the boat with dead batteries, ruined.

Agree with that.

But I'm not certain that a 1.5 amp charger will fully charge a 500AH
bank.

Have you actually done that? 1.5 amp charger charging a 500AH bank or
larger.

I'm guessing a 500AH bank would need at least a 5 amp charger to bring
it up to 14.2 volts and a fully charged state. A 1.5 amp charger might
bring it up to something like 80% charged before it can't up the
voltage above 13.2 volts or so, and just floats the partially charged
bank. Could be wrong though, anybody wanna chime in here with
firsthand experience?

I do agree a 1.5 amp charger will float a fully charged 500AH bank,
that's 36 amps a day, more than the natural discharge loss of the bank.
But will it charge it up from a deeply discharged state?