I use an unprotected CR2 rechargable from DX in a Ultrafire 606A.
It is SKU 932 and they are $3.70 for two.
If you wanted 2 good batteries i recomend buying 2 packs though. I only ordered one pack and one of the betteries was DOA. I check the voltage when first thing when I opened the pack and found one good battery at 3.2V and the dead one was only 1.6V. :fail:
The dead one is sitting on my desk and every time i look at it I wonder when/if it will go :poof: The good one has not had any problems. I use the light regularly and the run time is aprox. 25 minutes.