Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 40Get this manual
Battery Precautions
If hydrometer has built-in thermometer, draw liquid in several times to ensure correct temperature before taking readingHold hydrometer vertically and draw in just enough liquid from battery cell so that float is free-floatingHold hydrometer at eye level so that float is vertical and free of outer tube, then take reading at surface of liquid Disregard curvature where liquid rises against fl oat stem due to capillarityCAUTION
If attery ac id comes in contact wit skin or eyes, wash skin immediately with mild soapFlush eyes with wa-
ter Immediately and see doctorWhen charging batteries, an explosive gas mixture forms