2004 Official factory service manual for Yamaha YFZ450S ATV Quad., Page 129Get this manual
CHECKING AND CHARGING THE BATTERY Charging method using variable-current (voltage) charger
Measure the open-circuit voltage prior to charging
NOTE: Leave the battery unused for more than 30 minutes before measuring its open-circuit voltageNOTE: Set the charging voltage to 1617 V(If the charging voltage is lower, charging will be insufficient, if it is higher, the battery will be over-charged
Connect charger and ammeter to the battery and start charging
Is the amperage higher than the standard charging amperage written on the battery?