I also use the Streamlight UltraStinger for duty use, and a SF G2Z as a backup. I believe FNG & Onyx are right and go with a 3 cell (9v).
As a backup to my backup, I carry a SF Z3 Combatlight with a GG&G Tactical Impact Device attached. It'll produce 105 Lu for close to an hour with the P90 LA, but I prefer the P91 LA for that extra "punch." It's holstered on my war-bag along with a box of SF 123's. Sometimes, a DC charger just isn't practical out in the field and replacing the batteries is just a much better option.
The Z3 is available for about $83.00 (or you can still get the diminishing stock of D3 Defenders for about $93.00) at productwizard.com -
I'm thinking about upgrading to the M3, but I'm a fairly cheap *******, so if anyone has any suggestions that'll beat the $190 price tag, please please let me know. /ubbthreads/images/graemlins/wink.gif