A backup battery for any pwr modular product. Use this 3350Mah pwr bank as an additional battery for your pwr bike light, to charge your phone, watch, Garmin, Christmas mitten warmers...whatever device you like. We aren't the first to seek a better use of batteries. Think about power tools that have a universal battery system. Each device powered by the same battery is another opportunity to save. Save the environment, save space, save weight, and perhaps most important to you: save money. After all, batteries often make up over 50% of the cost of these types of products.