iphone 6s taking a long time to charge

I always charge my iPhone 6s on my PC. It normally takes about an hour or so to charge from 50% to 100%. Two days ago it took 4 1/2 hours to charge from 50% to 95%. I couldn't wait a minute longer so I unplugged it from the PC. I also noticed the rest of the day that the battery charge was not draining as normal. I used bluetooth, listened to music, lots of texting and made phone calls. By the end of the day,around 8 p,m. the battery charge was at 92%. This has never happened before. I contacted apple support and they ran a diagnostics but no problems were detected. Any ideas what might be happening? Troubleshooting tips? I welcome all. Thanks

PS: I made sure my PC's drivers were updated, ran an AV and malware scan, made sure windows update was current and ran a PC diagnostics. PC is not the problem.