Battery life

I am working from home. Unfortunately, I left the laptop charger in the office - I'm hoping I can get through the day without having to make the hour round trip to get the cable.

So, I'm keeping an eye on the charge remaining. The issue is that I'm faced with 3 percentages:

1. the battery icon in the system tray on the screen states that I'm on 100% (after 4 hours of use - I find this very hard to believe)

2. when I logout, on the sign-in screen, I'm told that I have 20% remaining

3. when I enter BIOS (when starting up), the number reads 95%

Which is correct?

I would rather not have to go back to the office :(