Unfortunately I was never able to find out, that's why I switched back to lead. My airplane is electrically dependent, and couldn't afford that uncertainty with my risk budget.
Just like the OP, I never completely discharged this battery, and when I ran the avionics for an extended period I always charged it back up with the approved Optimate charger.
There's one thing I think may have helped destroy the battery. A few months before I discovered the swollen battery I had a failed rectifier bridge in my alternator. Normally the EarthX maxes out the alternator after startup for a few seconds to a minute. I would see 60+ amps during that time. With the failed bridge (and a missing phase) it would only go to 40 amps or so.
These batteries don't seem to be liking pulsed power. See Rotax notes in the manual. My battery was 3 years old.
From what I understand, puffed cells are likely the result of an overvoltage event. There were none of those in my case. I have crowbar OV protection on my alternators, and OV audio alarms in my Efis. If a cell shorts out (there are 4 connected in series), the others will see a higher voltage and it will puff up the rest of the cells.
I wish EarthX would investigate these events more to come up with an improved BMS. They designed a great system, but maybe they haven't thought of everything.
There's a lot more to our diverse electrical systems than a benchtest setup. We have a bunch of load dump events, voltage spikes from solenoids, and the possibility of missing alternator phases that these cells might not like to be handling. Btw, I do have a load dump Mosorb in my RV-10, and all solenoids/relays are transient protected with TVS diodes.
Lenny
Lenny, any idea what might have caused this? Probably more a question for Kathy, but happy to get any hints or tips to avoid it on my little lifepo4.