One or more battery sub-modules are selected by obtaining at least one voltage from each battery sub-module and selecting based at least in part on the obtained voltages. The battery sub-modules are electrically connected in series in order to provide power to a primary load. Each battery sub-module includes a plurality of cells electrically connected in series and each battery sub-module further includes a battery management system that monitors the cells in that battery sub-module. Those battery management systems in the selected sub-modules are turned off so that the battery management systems in the selected sub-modules do not consume power at least temporarily from the cells in the selected sub-modules while (1) the battery sub-modules are not providing power to the primary load and (2) the battery sub-modules are not being charged.