I recently upgraded from an iPhone 5s to a 6s. Most days my phone battery lasts the entire seven hour work day easily (my 6s typically lasts about two days).
But now and again with the 5s I would have a day where it got really hot and the battery drained incredibly quickly. It wasn't due to use because I don't use it much during the day. I'd check the battery info in Settings and nothing in particular would stand out. My guess was something to do with the cellular signal strength in our office which is notoriously bad (WiFi is not an option in the office).
With the 6s I've been getting about two days out of every charge, but today I noticed at lunch time my phone was notably hot and the battery had drained about 70+%. So it's started doing the same thing. I turned on the low power mode and 2-3 hours later, even though I haven't used it at all, my battery is now down to single figures.
My question, is there anything I can do to confirm that the drain today was due to the problematic cellular signal? Is there something to look for in the "Diagnostics & Usage" data? I've seen a glimpse of the tools Apple use at the Genius bar to diagnose battery issues. Are there any Mac/iOS tools available to Joe Public that can talk to an iPhone to query diagnostic information?
Tried rebooting my phone before writing this question. In the time it took me to write the question (on a different machine) my phone battery dropped from 9% down to 6% while sitting on my desk ostensibly doing nothing.
TL;DR; Across two different devices most days my phones last the full work day with room to spare. But now and again I get a day where they only last half the work day. I think the problem is cellular signal strength. Is there any way to prove this?