The Basics of USB Battery Charging

By: Len Sherman

Abstract: Arguably the most useful part of USB's power capabilities is the ability to charge batteries in portable devices, but there is more to battery charging than picking a power source, USB or otherwise. This is particularly true for Li+ batteries, where improper charging can not only shorten battery life, but also can be a safety hazard. A well-designed charger optimizes safety and the user experience. It also lowers cost by reducing customer returns and warranty repairs. Charging batteries from USB requires balancing battery \"care and feeding\" with the power limitations of USB as well as the size and cost barriers ever present in portable consumer device designs. This article discusses how to achieve this balance.