I don't think it's the phones either, but mine is acting REALLY weird now. It dropped to 60%, I have taken 3 calls, and sent and received a few texts....It remains at 60%
I think I'm going to let it go completely dead (Still have my 4 so no worries about coverage) Then re-charge it and see what happens then.
I've recalibrated my battery multiple times. it will stay on 100% for about a good 10 minutes and then start dropping rapidly.