2007-2009 Yamaha F15/F20 Outboard Service Manual, Page 310Get this manual
4BATTERY SELECTION CAUTION:
Do not use battery which does not meet the recommended capacityIf different battery from recommendation is used, the electrical system may perform poorly or be overload, causing the electrical system damageSelect suitable battery by the table belowModel F15 (6AG) F20 (6AH) Recommended battery Unit Rating CCASAE Min245 amps MCAABYC Min323 amps RCSAE Min52 mins CCAEN Min347 amps 20HRIEC Min40 AH JIS 32C24-65D31