Surface Pro 3 battery degradation

I've been using Microsoft Surface Pro 3 for a year, and shortly after the warranty expired I noticed my Surface Pro 3 can only last about 1-2 hours after a full charge. At first I thought this was a problem with background process draining the battery so I disabled everything running in the background. It didn't helped. Then I found out about the powercfg utility and run powercfg /batteryreport on it, and this was the result:

A full charge capacity has degraded by over 80% in just few weeks and continue degrading. I tried to "recalibrate" the battery by doing full charge then full drain multiple times, and it didn't helped. Talk with Microsoft via chat support and they insist this was a software problem and reinstalled the driver and asked me to wait few days to see if things improve. Not only it didn't improved, but now my Surface can only last 30 minutes.

Few days after chat (today), I called Microsoft support and they were being extremely unhelpful. Insist that this was a software problem (which the chat support person already did) and it's "perfectly normal" for battery capacity to degrade. I insist that I've already done the software "fixes" and it didn't work and tell them this is definitely hardware problem, but the person on the phone tell me there's nothing I could do except to order the out of warranty exchange (which cost about $560 in my local currency). 

Is there anything else I should do? My country has no Microsoft Store which I could take the machine for them to take a look. Phone/online support were the only option, and none of them could understand the issue.