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 2500mAh for total power of about 10 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 won’t snag or get stuck in a matching jst jack, and 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 1200MA 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 – 1200MA max in this case. Even 500MA is a good charge rate, which is how much you can get from a USB port.