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 500mAh for a total of about 1.9 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 150mA or less. We suggest Adafruit’s Micro Lipo charger, which has a 100mA default rate. You can also set the Micro Lipo to 500mA rate for a faster charge. Like most lipos, the batteries we sell do not have thermistors built in. This is why we suggest charging at 1 C or even less – 100 to 500mA is a good rate, and available from any USB port if using a USB-powered charger 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. Details Weight: 10.5g Size: 29mm x 36mm x 4.75mm / 1.15″ x 1.4″ x 0.19″ Power Lead Length: 80mm / 3″ Output: 500mAh at 3.7V nominal