General

When it is necessary to charge the battery, the following conditions must be observed:
^ Use a constant voltage power supply with an end charge voltage of 16.0 volts-direct current (VDC) and equipped with a voltmeter that is accurate within 1%.
^ If more than one battery is to be charged, the batteries should be connected in parallel with each other; positive to positive (+ to +) and negative to negative (- to -).
^ Ambient (surrounding) temperature should be 15 to 38°C (60 to 100°F). A battery that is extremely cold may not accept current for several hours after charging has begun.
^ Charging area should be well ventilated.
^ Do not charge battery if the Built-In hydrometer is clear or light yellow. Replace the battery if this condition is discovered. Refer to "Built-In Hydrometer" for additional details. Built-In Hydrometer
^ Do not charge the battery if the electrolytes are frozen.
^ If the battery feels as hot as 52°C (125°F) or hotter, or if violent gassing or spewing of electrolyte through the vent holes occurs, discontinue charging or reduce the charging rate.