[Closed] Lumi XPG issue - any thoughts

Three year old Lumi XPG3 has been faultless until just before Xmas. Standard approach: charge battery, plug into light, make sure it's working, unplug until needed. When I plugged it back in it didn't power the light at all. No power at all. Plugged it back into the charger for 10 mins, started working again.

Then it failed again, plugging it back into charger didn't fix it, sent it to lumi who diagnosed it with a dead cell. Fair enough, spare battery has just started doing the same tho. It's brand new (if three years old, never used before Jan), worked fine first couple of times but did exactly the same last night. I 'reset' it on the charger and it's started working again, but I don't want to risk goosing a second battery.

Can't be a coincidence can it? Problem with charger and/or light unit? My mates (which is the same age) has started doing the same as well! Any ideas before I send the whole thing back to Lumi for a fettle?