Yamaha CS50 Service Manual page 59

CHECKING AND CHARGING THE BATTERY
Charging method using a constant voltage charger
YES
Charge the battery until the
battery's charging voltage
is 15 V.
NOTE:
Set the charging time at 20 hours
(maximum).
Measure the battery open-circuit
voltage after leaving the battery
unused for more than 30 minutes.
12.8 V or more --- Charging is complete.
12.7 V or less --- Recharging is required.
Under 12.0 V --- Replace the battery.
Measure the open-circuit
voltage prior to charging.
Connect a charged and
AMP meter to the battery
and start charging.
Make sure that the current
is higher than the standard
charging current written on
the battery.
3-29
CHK
ADJ
NOTE:
Voltage should be measured 30 minutes after the
machine is stopped.
NO
This type of battery charger
cannot charge the MF battery.
A variable voltage charger is
recommended.