Yamaha F100B F100C Outboards Factory Service Manual, Page 68Get this manual
Periodic checks and adjustments
Checking the battery
1Check the battery electrolyte levelIf the level is at or below the minimum level mark a, add distilled water until the level is between the maximum and minimum level marks
S60C3610
S60C3650
S60C3620
2Check the specific gravity of the electrolyteFully charge the battery if out of specification