Charge voltage is critical on these types of batteries because they both are recombinant batteries. This means that the oxygen that is normally produced on the positive plate in all lead acid batteries recombines with the hydrogen given off by the negative plate. The "recombination" of hydrogen and oxygen produces water, which replaces the moisture in the battery. Therefore the battery is maintenance free and never needs watering.
The sealing vent is critical to the performance of a sealed battery. The cell must maintain a positive internal pressure, otherwise the recombination of the gasses will not take place and the cell will dry out and not perform.
In addition, the valve must safely release any excess pressure that may be produced during overcharging, otherwise the cell would be irreparably damaged. It is because of the safety mechanism of the valve that overcharging hurts a sealed battery.
The excessive pressure that the valve is releasing is both hydrogen and oxygen. The more you overcharge a battery, there is less oxygen and hydrogen left inside the battery to recombine and create water. In essence, the battery dries out.
It's important to note that a sealed battery must never be opened once it leaves the factory. If opened, the cell loses its pressure, and the outside air will "poison" the plates and cause an imbalance that destroys the recombination chemistry.
Hence the name: Sealed, Valve Regulated (SVR) Battery.
The correct charging voltage for a Gel battery is 13.8 to 14.1 volts maximum at 68°F. The correct charging voltage for our Absorbed lead acid battery is 14.4 to 14.6 volts maximum at 68°F.