Battery Menu Bar doesn't show Time Remaining
I can think of several failures to cause that, but let's rule out the obvious.

Open terminal.app and type:

pmset -g pslog


The log will show what the power management subsystem is seeing from the SMC. After trying to connect power, disconnect power and seeing charge for 10 minutes and then off charge for 10 minutes, you should have a good understanding of what is or what isn't working.

At that point, try resetting your SMC one time. Make a note of the information as if that doesn't fix things it's likely a hardware service situation. 


https://support.apple.com/en-us/HT201295 - How to reset the SMC