255% available (plugged in)

I have the same problem and also since september update. Tried everything around October, couldn't find any solutions back then. Now I finally see this forum topic and it seems A LOT of people suffer from it.

Hi. I suddenly noticed the same thing after updating windows 10 today. So, after reading all the posts on this issue, I tried the unplug method described on thread page 3. However, as I was about to remove the battery, I noticed it had somehow become dislodged on one end. (Probably me twitching as I was getting over-excited watching footy on the laptop). On refitting it, then restarting it, the problem disappeared and is now showing 100% charged, as it should have been since it’s been plugged in for over 5 hours before it came loose. A loose battery isn’t something I considered to be honest! Therefore, I can only presume that when a battery is either dead, empty or simply not fitted correctly, it is displayed at 255% with a X inside the empty battery icon.) Never seen this before but then again, I’ve never had one end of the battery loose. This also makes sense as the laptop turned off as soon as I removed the power lead (before I refitted the battery and considering some have refitted or replaced the batteries, thus making a correct contact in the laptop, it may be as simple connection issue, or dead battery. Not really a windows update fault perhaps. Just a thought

I have solved the issue installing a little program called BatteryBar and disabling the Windows 10 icon!

I am very confused about this problem; I too see that 255% available when I hover my mouse on the battery as you can see here:

but if I click on it, It shows 100%.

but when I unplugged the charger; surface immediately went dead and won't turn on without the adaptor. 

I can't use it on battery.

I don't know when this problem starts, but I just noticed it today.

I have been working at home from the last couple of weeks, so the Surface Pro4 has been constantly plugged in. 

What happened? Does anyone have any clue?

I have a Lenovo Thinkpad Yoga X1, running Win 10. Till Jan 28th 2020, it was working fine. Suddenly on updating my laptop with the Jan 28 Win 10 updates, I started experiencing these weird issues of the battery showing 255% along with an x sign on it. My battery is connected and is not user replaceable, so no problem with a loose connector either.  To further complicate things, the machine was going blank and I had to literally shut the lid, then reopen and it would work. Sometimes, erratically after about 30 mins of working, it would self lock the machine.

Struggled for a few days, before finally uninstalling the Win 10 updates. Guess what, my machine is back to normal. Works just fine. There is a definite bug in the Win 10 OS. 

Surprised though that people have been experiencing this from atleast 2019. 

Suggest you try uninstalling the Win 10 updates and trying.