I replaced an exploded battery in a so-called Gen2 (pre 2008 but with electric stepper), which uses the 0A18010SRV, it had exploded the battery almost 2 years to the day earlier.
I think she is a candidate for installing a 0G8023 charger to work in tandem with the 1801 on her next maintenance. This eliminates the need to run an always hot 120 vac to the generator.
The 8023 gets its primary from the sensing fuses, and charges the battery the majority of the time. The 1801 (original) charger runs during exercise and during power failures, getting its primary from the dedicated winding in the alternator. The battery charger relay rewired to switch off the 8023 when the generator runs.
The 0A1801SRV and the 0G8023 are reasonably priced, easier to determine they are working. Search the part number on the Ziller store. Many aftermarket chargers will not keep the panel up if you disconnect the battery. Which is usually a sure sign you have a charger problem, if the display goes blank when you disconnect the battery. The generator should also run with the battery disconnected.
Original equipment also makes a much neater battery compartment. These aftermarket chargers are often screwed to walls with sharp screws sticking out and/or straps, and then tiny wires attached to the battery lugs, piles of ac cord, or spring clamps that get in the way of battery maintenance.
State your problem, not your diagnosis.