First your in the
MA2 thread, second never leave batteries in aircraft for this reason. There are reports of the M2 series turning on with defective batteries. People disagreed with me about storing batteries in aircraft and storing all batteries in case with with aircraft. Had your battery go "nuclear". It would have taken out all batteries and aircraft, but possibly and highly likely burnt down your home and then if happened dead of night?....you get the picture.
This is noted in a few threads about M2 batteries, no rhyme or reason why it happens to some and not others..other than trying to find out a batch date of batteries which not sure if that was ever established. If the aircraft is in warranty and possibly if battery is too, you can take a claim with DJI. They may even "listen" if outside of that warranty.
However I would imagine storing in aircraft and battery storage is mentioned in your owners manual that you should have read and anything done contrary to that advise would be on you...but doesn't hurt to at least try. 68° is too high to store a lipo though and coupled with the battery going to self discharge creating more heat might explain what happened.
Just bad storage on your part I am afraid to say IMHO. Battery Safety Guidelines, See line 4 of Battery Storage:
https://dl.djicdn.com/downloads/Mav...igent_Flight_Battery_Safety_Guidelines_EN.pdf