The easiest way to rate the percentage charge on an absorbed glass mat deep-cycle battery is to use a multimeter. If a multimeter isn't available, the percentage charges and corresponding voltage rates for AGM deep-cycle batteries according to RV Solar Connection are 100 percent charge equals 12.9 volts, 75 percent charge equals 12.6 volts, 50 percent charge equals 12.3 volts, 25 percent charge equals 12 volts and zero percent charge equals less than 11.8 volts.Continue Reading
AGM deep-cycle batteries are lead-acid batteries that are marketed as maintenance-free, which means you don't have to add water to them periodically like older batteries. These batteries are often sealed and don't contain any removable caps through which water can be poured. However, just like traditional batteries, they still need to be well-ventilated to continue to function well. If an AGM deep-cycle battery no longer holds a charge, it is time to replace it.
AGM batteries use a fiberglass separator to hold the electrolyte in place between the lead plates. This lends the battery greater structural integrity, allowing it to remain stable and fully functioning whether it is installed upright, sideways or upside down. AGM batteries can last longer than traditional or gel-cell batteries and can match wet-cell batteries in terms of performance and charge rate.
It is important not to confuse AGM deep cycle batteries with ordinary maintenance-free batteries, as the latter does not hold up to repeated discharging.Learn more about Car Parts & Maintenance