Do not put in two CR123 batteries in there. It will most likely fry your circuit board. The voltage of one CR123 is the same as one 18650 (3.6 volts) If you put in two 123s you will be putting 7.6 volts to your driver.

I am not sure which P7 you have, but most sold at DX have a max voltage of 4.2 (which would be about the voltage of a freshly charged battery)

You could buy a black and decker lithium battery pack, crack it open and harvest the two batteries inside. Most stores are closing them out at under $12.00 from what I have seen. I have not done this, so I do not know if they are the flat top batteries or the button top. But for only $12.00 it maybe worth a shot. You will still need a charger that charges the lithium batteries.