I had a similar issue with battery wear. Just started dropping after about 14 months. Lots of chatting with MS support. They remote accessed my machine to try a few things. No luck.
Fortunately I had extended care and was able to get a new machine (brand new). However, it was a Windows 10 machine so I lost my Windows Media Center capabilities (no more DVR) and of course the new OneDrive doesn't have shadow copies like the one on Win 8.1 so I'm not overly happy about those two items. But, support was very good about shipping a replacement, so no complaints there.