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 a total of about 10 Wh. If you need a smaller battery, we also have a 1200mAh model

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, 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 ~2.8V. 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.

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. Never charge or use unattended. Always inspect batteries and surrounding circuitry constantly for any damage, loose wiring, or the possibility of short circuits. Polarity matches all Adafruit LiPoly/LiIon chargers and boards, other brands may have reverse polarity and can destroy your battery. 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.