These 17670 rechargeable lithium batteries will keep you from having to buy expensive lithium batteries over and over. Each 17670 is 3.7V and 1800 mAh in a resting state. A protection circuit is attached to the battery to ensure that you do not overcharge or over discharge the battery. 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.