Yamaha Outboard Motors Factory Service Manual F6 and F8, Page 136Get this manual
GENERAL DO NOT SMOKE when charging or handling batteriesKEEP BATTERIES AND ELECTROLYTIC FLUID OUT OF REACH OF CHILDREN
Batteries vary among manufacturersTherefore, the following procedures may not always applyConsult your battery manufacturer's instructionsFirst, disconnect the negative lead, then the positive leadCheck: Electrolyte level Below the minimum level Add distilled water to the proper levelElectrolyte specific gravity Less than specification Recharge the batteryElectrolyte specific gravity: 1.280 at 20C (68F)