Abstract: A stackable modular battery pack system is disclosed that includes at least two modular battery packs, including first and second battery packs. Each of the modular battery packs comprises a case in which a battery is disposed, first electrical contacts electrically connected to the battery and disposed on an exterior of the case, and second electrical contacts electrically connected to the battery, with the second electrical contacts being disposed on the exterior of the case. The case of the first battery pack is configured to releasably engage the case of the second battery case. The first electrical contacts are located on the first battery case and the second electrical contacts are located on the second battery case so that the first electrical contacts contact the second electrical contacts where the case of the first battery case and the case of the second electrical contacts are engaged.