The DustBusters I have had (which have two removable battery inserts, which I believe use sub-C cells) have not survived well. A year or two sitting on the trickle-charger (as designed) and the NiCd batteries are toast.
I've been thinking seriously about tearing it open, and replacing whatever simple fixed-resistor slow-charge circuit it has with a proper faster-charge-and-real-cutoff circuit of some sort. I'd have to replace the wall wart, most likely, to get a decent charging current.
Seems like there ought to be a single-IC solution available today... and if not, something simple with a PIC or other micro to switch from full-charge to "off most of the time, very brief current burst every few minutes to cancel out self-discharge" should be able to do it well enough.