CAUTION
Always connect the battery charger according to manufacturers instructions.
Generally, a battery should be charged at a slow rate to keep the plates inside from getting too hot. However, if some batteries are allowed to discharge until they are almost "dead", they may have to be charged at a high rate to bring them back to life. On maintenance-free batteries it may be necessary to tip the battery from side to side to get the built in hydrometer "eye" to register it's green color after charging.
Charge the battery at the proper charging rate (amps) and time span.
CAUTION
Batteries naturally give off a certain amount of explosive hydrogen gas, more
so when they are being charged. Keep any flame or spark source away from batteries
at all times. Do not charge the battery for more than 50 amp/hours (to figure
this, multiply the amps of the charging rate by the number of hours). If the
green dot appears, or if electrolyte squirts out of the vent hole, stop the
charge.