As it relates to SENS chargers, we do not recommend the NRG or FC/A chargers on VRLA (AGM) batteries WHEN there is a continuous DC load (> ~2 amps DC) applied to the charger and battery bank. The reason for this restriction is that the combination of the charger's charging and the continuous load discharging, alternately charge and discharge the battery at two-times the AC line frequency. This alternating fast charge/discharge can mechanically damage the VRLA battery and shorten its life.
In contrast, when there is little or zero continuous DC load, as is typically the case on engine starting batteries, only minor discharge occurs between charging pulses. Such minor discharges do not typically shorten battery life, and VRLA batteries can safely be used with SENS unfiltered (NRG, FC/A) chargers.
If your application does have a continuous load (>~2 amps) applied to the engine starting batteries, then we would recommend an ECU Series (filtered) charger.
Note: One additional practice that SENS recommends is the disabling of the auto-equalize function on non-filtered chargers, so that a lower charging voltage is applied to the batteries to further reduce the possibility of gassing. Since VRLA or AGM batteries have very small amounts of electrolyte, it is safer to operate them at lower charge voltages. Unfortunately, the FC/A chargers do not have the ability to disable the auto-equalize function. The NRG charger does have this ability by repositioning a pin jumper.
For questions regarding specialized applications of battery chargers, please contact Davidson Sales Company.