occasional gas build up in ET P20 A2

My EagleTac P20A2 (with GREEN LED) has been a much used excellent purchase. Im using decent NiMH cells eneloop, tenergy etc. A few weeks ago and again this evening it fell over while tail standing beneath a desktop lampshade. I noticed and felt the rubber tail cap protruding and bulging. what little I know about gas build up in metal flashlights told me to unscrew the head (while standing behind a door) then the bulge was gone. I changed cells, no problem, until this evening when it happened again. This time because the cells still appeared to have ample power I removed the head then replaced it with the cells still inside. 10 minutes later the tailcap bulged out again I removed the cells and put in freshly charged cells. ANY thoughts on what's going on here? thanks!

Does it work with *alkaline* batteries? I don't recommend them because they leak, but just as a test. I suspect the batteries or the charger. Measure the voltage of the cells fresh off the charger. If the cells work in other lights and charge normally, I would email EagleTac and describe the situation. They may have an idea. I have several EagleTac lights and have never had a problem.... (with lithium ion cells).

I had a similar problem in my E01 using a lithium iron cell. I could hear a slight soft pop when I opened it up & it scared me. The last thing I wanted was to EDC a pipe bomb. The E01 is sealed very tight & does not allow gases to escape. I switched to Eneloops & have not had any problems with them. Is it possible your charger might be overcharging the Eneloops? I have never had a problem with mine.