When used with a properly regulated constant voltage charging system (such as an alternator), the OPTIMA battery will normally not produce hydrogen gas. Occasional gassing can occur when charging at higher voltage levels or in extreme high temperature conditions. In automotive applications this typically will not happen if the alternator/regulator stays below 15 volts.
 

1st OPTIMA Battery Sales ships OPTIMA batteries to the U.S. 48 states with Free Shipping.