A portable charging case is provided. The case includes a charging interface configured to establish a power transfer connection with a wireless audio device having a battery. The case includes charging circuitry configured to determine a voltage of the battery. The charging circuitry is further configured to, if the voltage is less than or equal to an undervoltage lockout, charge the battery in pre-charging mode. In pre-charging mode, the charging circuitry is configured to apply a constant pre-charging voltage to the battery. The charging circuitry is further configured to switch from pre-charging mode to standard charging mode when the voltage exceeds the undervoltage lockout value. The charging circuit is further configured to determine the voltage by (1) powering on, via a case power source, the wireless audio device; (2) applying, pre-charge load to the device battery; (3) retrieving the voltage; and (4) transmitting the voltage to the case.