Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 71Get this manual
Battery Precautions
1Hydrometer must be clean (inside and out) to insure an accurate reading2Never take hydrometer readings immediately after water has been addedWater must be thoroughly mixed with electrolyte by charging for at least 15 minutes at rate high enough to cause vigorous gassing3If hydrometer has built-in thermometer, draw liquid in several times to ensure correct temperature before taking reading4Hold hydrometer vertically and draw in just enough liquid from battery cell so that float is freefloatingHold hydrometer at eye level so that float is vertical and free of outer tube, then take reading at surface of liquidDisregard curvature where liquid rises against float stem due to capillarity
If battery acid comes in contact with skin or eyes, wash skin immediately with mild soapFlush eyes with water immediately and see doctorWhen charging batteries, an explosive gas mixture forms in each cellPart of this gas escapes through holes in vent plugs and may form an explosive atmosphere around battery if ventilation is poorThis explosive gas may remain in or around battery for several hours after it has been chargedSparks or flames can ignite this gas and cause an internal explosion which may shatter the batteryThe following precautions should be observed to prevent an explosion1DO NOT smoke near batteries being charged or which have been charged very recently2DO NOT break live circuits at terminals of batteries because spark usually occurs at the point where live circuit is brokenAlways be careful when connecting or disconnecting cable clamps on chargersPoor connections are common cause of electrical arcs which cause explosions3DO NOT reverse polarity of battery terminal to cable connections