I know plsvn but in your specific case your battery was defective long before the iOS was released. Issues in China were reported while still in iOS 9 and they was a major push-back by Chinese regulatory authorities - threatening to stop the sale! Apple did its diligence to seek the issue, isolate it, release diagnostics tools, and issued the recall which covered you. But in the PRC thousands rapidly were shutting down while in iOS 9. So there is an organic link between the factory defect (Lithium stored in the open), programming, tools, coding and shutdown parameters. Do you remember when we used to modify motherboard multiplex parameters to get more voltage and increase CPU frequency = higher CPU processor speed for gaming? All we were doing is alter the BIOS coding parameters, made easy by motherboard manufacturer. And we were told to raise the mHz frequency 5% no more per shot until the system became unstable, which told us our max ranges..
So any iOS comes with different amperage parameters- I think it intuitive with anyone. unfortunately, the most unstable element of these devices is that electrolyte Li Ion gel, LiFePO4 or LFP, (in your case, factory defective). Every other component in an iPhone is like a tank- solid and years worth of usage. As soon as a new amperage is demanded, this gel can just fail. Electrons can go haywire while traveling back and fourth between the cathode and the anode. It can happen with an install, or 5 cycles into a new install. Think of it as a battery neurological disease, always progressive and worse.
the real issue here, which tech journalists are exploring aggressively, is why were there those 6S batteries recall an issue, and why some 12+ months old batteries really dislike the upgrade the same way as the recalls. The industry tells us that these batteries have a 300-500 cycle range. At 1.5 cycles per day, it is 550 cycles in 12 months. After that, the electrolyte is one surge away from going bad. I wish this was not the case, wish they were better (my employer's satellites use 8000 cycle-rated Li plates and electrolytes). Unfortunately, may very well be a reality we do not want, but here for the moment until consumers make their discontent known.
A good analogy is a good GT car daily driven, take it at a track and redline it 200 kms, there is a good chance the engine will blow. yet the car works perfectly, daily driven. But the stress margin of failure is high under load. To prevent that, FIA allows 9 engines a year and teams rebuilt them before every such stress, and tests the components one by one. We do not do that with phones, we just load a new iOS, which is a new racing circuit. As a rule, BTW, I now wait 3-6 months before deciding on any OS upgrade, mac or mobile device.
the future is here though:
http://www.computerworld.com/article/3060005/mobile-wireless/scientists-can-now- make-lithium-ion-batteries-last-a-lifeti…