battery capacity indicator button not working
Your indicator light seems broken and is pretty much hardwired. Did it ever see any moisture? Replacing it is a relatively difficult procedure, as seen in this video. You will find more guides on iFixit (e.g. this one) explaining how to get to the Battery Indicator Light. But I don't know where you could get a new one if yours is broken.

If you are looking for a terminal command to get your current power status, use pmset. pmset -g batt will tell your the current power source and remaining battery capacity:

$ pmset -g batt

Now drawing from 'AC Power'
 -InternalBattery-0 99%; charged; 0:00 remaining