Yamaha DT125E 1977 Owner's Manual page 45

Battery
Check the level of the battery fluid and see if
the terminals are tight. Add distilled water if
the fluid level is low.
Replenishing the battery fluid
A poorly maintained battery will deteriorate
quickly. The battery fluid should be checked
at least once a month.
1. The level should be between the upper
and lower level marks. Use only distilled
water if refilling is necessary.
1. Upper level 2. Lower level
NOTE:
Normal tap water contains minerals which are
harmful to a battery; therefore, refill only
with distilled water.
2. When the motorcycle is not to be used for
a month or longer, remove the battery
and store it in a cool, dark place.
Completely recharge the battery before
reusing.