Old cr*apped out batteries will cause constant device shutdowns at heavy load!
I hate Apple. Really, REALLY hate them. But... when I wiped the multigigabyte virus called Windows 10 from my i5 laptop (it had installed inself while I was away enjoying coffee one afternoon), installed Windows 7 Professional and set everything to max while on battery as a power plan: screen 100% brightness, CPU 100% performance at all times, Hard Drives at 100%, WiFi 100% etc... the battery couldn't cope and the thing would simply switch off because it was incapable of providing the amps. My battery would only charge to 98%. F*cked it was. Imagine the uproar if all users of older iPhones experienced something like this whenever they upgraded their OS. Also, constantly switching it back on again and again right after it failed could also cause the battery to overheat and explode. That would certainly be a horrible "customer experience". Sorry, I'm with Apple on this one... bleug! (runs away to jump off the roof onto heavy traffic)...
...(survived) At least with my Asus laptop, I can replace the battery and sort the issue, and do so conveniently and cheaply. For all the jesusness of the jesusphonne they do seem to have it in for mother earth. Wouldn't happen in a pagan company.
Explaining to users about the reasons why would have diminished the jesusglow. Apples "just work" don't they? Saints Paul, John, Luke and Erik would be p*ssed they had to think about something.