Various techniques described herein relate to battery packs of electric vehicles, batteries, and battery charging systems. Batteries may comprise a plurality of battery modules, wherein each battery module may be provided with one or more battery cells, and the plurality of battery modules may be connected in series when providing electric power output. Battery charging systems described herein may comprise a charging circuit that connects a plurality of battery modules in series, and may be used for charging the plurality of battery modules in the battery in series. Additional charging circuits may be connected respectively to the plurality of battery modules, and the additional charging circuits may be used for charging at least one battery module in the plurality of battery modules.