I have been storing lipo's for long periods at 50% charge with no problems some are now six years old with no sign of swelling, in fact some of the old original phantom batterys are still good with possibly upto 5 minutes less flight time than when new, Typhoon H batterys have been stored the same and have not been used for at least 18 months, recently I charged it up and took the H out for a flight just to make sure everything was still good which it was with no degrading of flight times from new, I have only had the MPP for a few months now so not long enough to judge the DJI mavic Pro Platinum batterys yet but they get stored the same with 50% charge, also in use I never go below 30% discharge with all my battery's, I only leave them fully charged for a 2-3 days at maximum it not used they are discharged to 50% storage capacity, my storage for all my batterys is a unused fully enclosed log burner fire indoors which still has the stainless flue chimney connected, but the fire is no longer used and was left in situ just for looks and for me this has proved the ideal safe storage space the temperature does not fluctuate to much summer or winter inside the fire, and if something should ever happen the flames and smoke will go up the chimney and not burn the house down.
I also never charge any batterys above the 1C rating for any given battery although a lot of my older batterys have been parallel charge but still not above the combined 1C charge rate.
My own thoughts of any swelling lipo's is more than likely caused by a several factors, running the battery down to low causing the battery to overheat leading to premature failure, not allowing any lipo to cool down between flights and then recharging them, crashing your craft could also cause unseen damage at the time to the lipo battery, never leave lipos in a parked vehicle the during the summer months to that matter never leave anywhere that gets hot whether direct sunlight or otherwise any such extreme heat will puff the battery, charging them on a quick charge will also shorten the battery life by a fair bit, others may disagree with my statement of causes but in all my years of flying RC models and last six years flying drones I have only ever had one battery puff up and that was caused after parallel charging I accidently shorted one of the leads whilst disconnecting one battery which was purely my own fault.
