Disclosed is a charger device. The charger device includes a housing, defining a volume, that includes a power conversion module to provide output power of between 3-300 W, and a controller configured to determine a current level to direct to one or more rechargeable batteries, and cause the output power to be directed to the one or more rechargeable batteries at a charging current substantially equal to the determined current level. A ratio of the output power directed to the one or more rechargeable batteries and the volume is equal to at least 10 W/in3.