A high frequency battery charger for charging a target battery is provided. The battery charger includes a charging circuit including a high frequency transformer, a switch switching the high frequency transformer, a filter coupled to the high frequency transformer for passing a DC voltage signal and a controller providing a high frequency driving signal to the switch. Measuring circuitry measures at least one of a voltage or a current at the target battery. A microprocessor receives the measured voltage or current and calculates diagnostics of the target battery based on at least one of the measured voltage or current.