My 6s battery has gotten pretty lackluster, and after severe battery issues with previous iPhones, I keep a close eye. This past week I have had insane fluctuations in capacity from as low as 65% of original to its usual spot of about 89%. This problem seems to only be getting more extreme and today it has pretty much stayed in the mid 70s but actually just crept back up to 89%. I know it needs to be below 80% for a warranty claim. My question is if I took it to Apple, what is their procedure for determining battery capacity? My concern is when they check it, it will be in one of its increasingly rare above 80 capacities. I go out of warranty September 25th and I would really like a battery replacement because these radical fluctuations are new and I do not see them getting any better. P.S. I am only at 393 cycles.