As I said in the other thread, I like each piece of my EDC to be as versatile as possible. Instead of using multiple devices to get the redundancy of multiple batteries, I'd carry one device and some spare batteries. A spare mobile phone battery may be expensive, but it's generally cheaper than another device that includes a battery, and it takes less room. (Plus I can generally afford to pay to reduce weight and volume in my EDC.)

I try to avoid devices that have batteries that can only be charged.

I am willing to put some effort into monitoring battery levels, and prioritising applications of multi-use items. I wouldn't lose use of the phone by over-using its camera. If I had to, I'd switch the phone off and just turn it on when I needed it, and rely on store-and-forward protocols such as text messages and voice mail.