...the battery yourself. They are available for under $100.
I bought my Surface Pro 4 (SP4) in November of 16' for personal use. As I have an issued work laptop for home use, I have not used my SP4 very much. The last several times I used my SP4 I recall hearing a strange "electrical" click sound at random times, whether I was using the device or not. A situation where you hear the sound and you glance at the device, it does not repeat at that time so you continue on with whatever you were doing. Now to more recent attempts to use my device. The SP4 will not work at all, unless it is plugged into the supplied AC power supply. The SP4 states the battery is at 87% and Not Charging". The device instantly shuts off if you remove the power supply. In other words, the battery is a complete failure. After researching the power issue in the MS forums and other sources, I installed the Surface Troubleshooter and this did not identify the issue, because when you get to the point in the program where you are required to "remove the AC power supply", my device shut off as it had been doing. After that, I worked with a MS technician yesterday to troubleshoot the device. The technician remote connected to my SP4 and ran through several checklists, that included software removal, update removal, reloads, restarts and other tests. During these tests the technician pulled up the power/battery information for the device. After ONLY 64 Battery Cycles, yes 64, the technician tells me that she is sorry, but my battery is shot. The batteries in these devices should be capable of hundreds and hundreds of battery cycles. The only solution she stated MS could offer was to replace this barely used device with a refurbished unit with a 3 month warranty, for "just $450.00 USD", which is close to half of what I invested in the original SP4 without accessories. Now for a device that is supposed to be top notch, is barely out of warranty, and was an expensive investment for me that I did a good bit of research on before making the purchase, I find this situation to be ridiculous! My SP4 has never been mishandled or abused. I have taken good care of it and kept it safely stored when not in use. It literally still looks brand new, as it has barely been used. To me, this situation, along with the MS solution is INSANE! There is no way that this should be acceptable. To say I am disappointed in MS, would be a gross understatement. This will forever change my opinion of Microsoft, and will adversely affect any future purchases by me, or anyone I can share this unacceptable experience with.