The battery no longer works but I’ve kept it plugged in and used it for streaming music at work the last few years. Today it’s in an infinite loop of rebooting and I noticed the glass popped out!
From what I see in the Internet, your battery is on the edge of exploding, bursting into extremely hot flames, and/or releasing toxic gases. You should unplug it and stop using it.
I see a few things indicating that an Apple Store may replace the battery (or swap the device) for free, but others saying the might charge you a the same as they charge for a battery swap.
Here are some links:
https://www.ifixit.com/Wiki/What_to_do_with_a_swollen_battery
https://mactech-solutions.com/beware-the-bulging-battery-and-what-to-do-if-yours-expands/
A puncture can cause the battery to swell, vent gas, or catch fire. If you have a punctured battery, store it in a fireproof container in a well-ventilated area. The gas that these batteries give off if punctured is toxic and flammable. The fire that can be produced is considered Class B, so keep a Class ABC or BC fire extinguisher on hand in case of fire. Contact a local hazardous material disposal center or e-waste facility to see what disposal options are available in your area.