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.
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 possibility of short circuits. 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.