Oh, it's not the battery that'll shorten the lifespan of the 5X and the 6P. It's the CPU. I've already had to replace my 5X under warranty twice. The second time was because of the bootloop problem, which will happen to every single device equipped with the Snapdragon 808 eventually.

My phone is basically living on borrowed time. And honestly, the next time it dies, I'm done with high-end devices. Having had to replace my phone twice in under two years has convinced me that I should treat my phones as if they were disposable, and so I'm going to buy my next phone at "disposable" prices. My next phone will probably be a Moto E4 or something in a similar price range (and I'd be willing to buy a $50 Chinese shitphone if only I could find one with AOSP and not some shitty custom UI).