These RCR2 (15266) rechargeable lithium batteries will keep you from having to buy expensive lithium batteries over and over. Roughly the same size as CR123 batteries, each RCR2 is 3.7V and 600 mAh in a resting state. No protection circuit is on these, so be very careful not to overcharge or over discharge these batteries. As with all lithium batteries, the proper care needs to be observed. Do not overheat, incinerate, reverse polarity, mix voltages, or do any other potentially dangerous activity with these or any other lithium batteries.