So, I got my external battery and decided that I would try it out each day by only using the external battery to recharge my iPhone 5 whilst out and about rather than using a mains power source or a PC or something similar.
I started the day fine. My battery was at 100% at 7am and I used the device normally. About 2:30 or 3pm it had dropped to 20% so I connected the external battery. I switched it on and all was good. I kept a close eye on both the iPhone and the battery as I’d heard about issues with overheating, but I had no such problems at all. In fact, the entire process was completely smooth and incident free.
Once the time the iPhone 5 had gone back up to 100% I disconnected the battery, which was still showing 4 bars (actually circles, but it means the same thing).
We’ll see how the process develops tomorrow.