According to :
One tip on DeWalt 9.6V drill packs. Wal-Mart sells the B&D packs for
less than $25. You need to cut the "keys" to fit drill and charger,
but they work fine.

Something similar but slightly with DW 12V and B&D "firestorm" 12V packs
(in a rebadged product). The keying is identical. The difference is that
the B&D packs exposes the shell of the battery in the "stem" of the pack,
and the B&D charger has a sensor contact that makes contact with it.
The DW doesn't have this.

The B&D charger won't charge the DW packs, but the DW charger
will do both. It became a bit of a nuisance when I had one of
the B&D packs rebuilt, and they didn't shave the cardboard off
the shell for the B&D charger contact. I could shave it off myself,
but so far I've not needed to.

[The B&D charger is _much_ heavier than the DW - the B&D has
a big transformer. The DW has a switching power supply, so it's
an itty-bitty toroid.]
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.