Lithium ion polymer (also known as 'lipo' or 'lipoly') batteries are thin, light and powerful. The output ranges from 4.2V when completely charged to 3.7V. This battery has a capacity of 900mAh for a total of about 3.3 Wh. The batteries come pre-attached with a genuine 2-pin JST-PH connector as shown and include the necessary protection circuitry. Because they have a genuine JST connector, not a knock-off, the cable wont snag or get stuck in a matching JST jack, they click in and out smoothly. The included protection circuitry keeps the battery voltage from going too high (over-charging) or low (over-use) which means that the battery will cut-out when completely dead at 3.0V. It will also protect against output shorts. However, even with this protection it is very important that you only use a LiIon/LiPoly constant-voltage/constant-current charger to recharge them and at a rate of 500mA or less.Like most lipos, the batteries we sell do not have thermistors built in. This is why we suggest charging at 1/2C or even less - 500mA max in this case which is how much you can get from a USB port. Additional safety notes: Do not use a NiMH/NiCad/lead-acid charger! Also, do not abuse these batteries, do not short, bend, crush or puncture. As with all Lithium ion polymer batteries and with any power source - they should be used by experts who are comfortable working with power supplies. Output: 900mAh at 3.7V nominal Connector: 2-pin JST-PH Cell dimensions: 48x30x6 mm