There isn't a "root issue". People have gone over this ad infinitum. The "root issue" is iPhone batteries like most cell phone batteries do not last more than several hundred recharge cycles and especially when under high load the power will be insufficient to maintain full phone performance without the phone suddenly shutting off. On Android your phone simply shuts off on high load on old batteries. Apple gracefully fails rather than hard crashes. This is a good thing, not a bad thing. Apple gave out free upgrades because people perceived it as if Apple had done something wrong so out of good will they gave free upgrades. Current phones will do the exact same thing given time.