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I think it’s a lottery. You can get good batteries and you can get bad batteries. Yes, charging slow and keeping your phone from getting hot can do a lot to help preserve the battery life you’ve been given - but it won’t do much if you got a bad battery from the factory. I’ve had some batteries hold their % for nearly two years, and other batteries drop like bricks within a 2 year timeframe. My 12PM held its charge for the year I had it. My wife’s 12PM dropped like a brick but she did use MagSafe a lot (usually our batteries mirror each other despite her being a heavy user and me a light user).

When we got our 13PMs - my wife noticed her phone burning so hot she could barely touch it using MagSafe - so, no more MagSafe for her.

How would it benefit Apple to put cheaper batteries in its devices? All it would do is piss people off and spread bad press. I’ve found my Apple devices usually have better batteries in them than most other devices I have with a battery. I’ll never forget my Samsung Note 3 losing 50%+ capacity in 6 months (rooted).

Older devices tend not to be used as much as devices today (my opinion) - helps them retain their capacity a bit more. Again, one can get a bad battery from the factory, others can get amazing ones.
 
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