Why are GEL and AGM batteries so charge sensitive and why is charge voltage so critical?
All lead-acid batteries give off hydrogen from the negative plate and oxygen from the positive plate during charging. VRLA DRY CELL AGM and GEL batteries have pressure-sensitive valves. Without the ability to retain pressure within the cells, hydrogen and oxygen would be lost to the atmosphere, eventually drying out the electrolyte and separators. Voltage is electrical pressure. Charge (ampere-hours) is a quantity of electricity. Current (amperes) is electrical flow (charging speed). A battery can only store a certain quantity of electricity. The closer it gets to fully charged, the slower it must be charged. Temperature also affects charging. If the right pressure (voltage) is used for the temperature, a battery will accept charge at its ideal rate. If too much pressure is used, the charge will be forced through the battery faster than it can be stored. Reactions other than the charging reaction occur to transport this current through the battery – mainly gassing. Hydrogen and oxygen are given off faster than the recombination reaction. This raises the pressure until the pressure relief valve opens. The gas lost cannot be replaced. Any VRLA DRY CELL AGM or GEL battery will dry out and fail prematurely if it experiences excessive overcharge.
What will happen to my DRY CELL AGM or GEL battery's life if the charge voltage is not controlled?
You will reduce the life of your battery by between 5% and 7% for every 1/10th of a volt above the recommended charge voltage. For example, if you continually charge your battery at a temperature-compensated value of 14.60 volts when it should be at 14.20 volts (4-tenths over), you can expect to reduce the life expectancy of your battery by 20% to 30%. As mentioned, DRY CELL AGM and GEL CELL batteries are voltage sensitive. All batteries are voltage sensitive. If you continually charge your Discover battery over the recommended voltage levels, you will shorten the life of your battery.