But now it is on my workshop floor and in June will have been there for 3 years. mostly shallowly cycled.
Not sure whether just shooting the battery lid with IR gun inbetween cell dividers, will show the whole story with an AGM.
Right! A more localized diagnosis can be found by using hands and fingers on the case sides.
A handheld meter is also more focused than relying on a battery meter.
For those pushing big amps into batteries, I'd recommend placing a milk carton and board or even a cardboard box over the battery while charging thusly. If the battery has a short and blows its top, some containment is better than no containment.
Good luck to those with misbehaving batteries!