Polymer Lithium Ion Battery is a very slim, extremely light weight batteries based on the new Polymer Lithium Ion chemistry. This is the highest energy density currently in production. Each cell outputs a nominal 3.7V at 1000mAh. These batteries require special charging. Do not attempt to charge these with anything but a specialized Lithium Polymer charger. Battery includes built-in protection against over voltage, over current, and minimum voltage. Please use caution when using this battery in wearable projects. When using conductive thread, a short in the thread can create sparks and heat. We recommend using coin cell batteries for beginners.