On Tue, 31 Jul 2012 21:27:06 -0400, "Stormin Mormon"
wrote:

From what I've heard, low but not totally dead. Some cells will exhaust
first, and the weak cells will be damaged.

For NiCds (probably what these are), not so low. ...but you're correct,
recharge them at the first sign of the tool slowing. They can be topped off
before storage, too, but not left in a (dumb) charger.