Larry wrote:
"Mark" wrote in news:1156734601.788399.316510@
75g2000cwc.googlegroups.com:

Isn't any portion of a plate which has dried out, permanently damaged
and unchargeable? The rest of the "dead" battery may be rechargeable,
but the battery's capacity is reduced.

Nope. It just lost contact with the electrolyte, so is unable to be in the
current stream to recharge. As electrolyte is recovered in charging, it
gets deeper, so we don't want to fill a discharged battery because it will
overflow by the time charging has recovered it.

I understand that a discharged battery shouldn't be topped of with
water for that reason, but it's my understanding that once a plate is
exposed to air and dries, it is irreversibly sulfated and will not
contribute to the battery's capacity again.

From a University of Washington paper:

"If plates are exposed above the electrolyte then the capacity of the
exposed plate
areas has been lost and cells will likely develop short-circuits
because of plate shedding. Batteries with exposed plates should be
replaced."

You seem to be saying exposed plate area can be recovered by
recharging. That's apparently not so. I once accidently exposed about
50% of the plate area on a battery, and it lost about 50% of its
capacity; soon thereafter it died due to shorted plates, probably from
plate shedding. Exactly as the UW paper described.