Battery packs according to embodiments of the present technology may include a first battery cell including a lithium-containing material. The first battery cell may be configured to operate in a voltage window extending to or above about 4 V. The battery packs may include a second battery cell electrically coupled in parallel with the first battery cell. The second battery cell may be configured to operate in a voltage window maintained at or below about 4.0 V. The battery packs may also include a controller configured to receive a measured terminal voltage from the first battery cell. The controller may be configured to determine whether to disconnect the second battery cell from the first battery cell based on the measured terminal voltage of the first battery cell.