During the charging phase it was 16.4 volts (2 volts more than the yuasa charger specification in the manual; overvoltage can damage the battery). Technical data: Maximum charging voltage 14.4 volts, but under maintenance. The voltage is 13.5 volts (which is correct). I used a flute multimeter. Please measure the charging voltage and confirm before it's too late. I received a refund from Amazon.