How do I check the health of my battery on my MacBook Pro?

There is no ideal option for checking the health of a battery anymore since macOS 10.15+ since the battery condition will either be "Normal" or "Service Recommended" where the latter has several different meanings, but no good way of telling what triggered that condition. Apple tends to hide the details in various places instead of making them readily visible.

You can try running the Apple Diagnostics to see if any hardware issues are detected. You can also use a third party app such as Coconut Battery which can show you the current capacity of the battery as related to its original Design Capacity. This app is really what Apple should be providing to us instead of hiding the details in various places.

If you get a "Service Recommended" condition and the battery capacity is over 80% of design capacity, then it usually means there is a hardware issue with the battery. Also if the Apple Diagnostics don't report a battery failure, then just use the laptop until the battery no longer meets your needs and then have the battery replaced by Apple or an Apple Authorized Service Provider. Unfortunately some battery failures are not detected by the diagnostics and some battery issues will only be detected at certain charge levels.

If you are using macOS 10.14 or earlier, then "Service Battery" indicates a hardware issue has been detected with the battery. "Replace Soon" indicates the battery capacity has dropped below 80% of design capacity, but may still be perfectly fine for many people depending on how the laptop is used. A "Replace Now" condition indicates the battery capacity is severely limited and probably won't run on battery power for very long and most likely should be replaced.

Hold down the option key and click on the battery icon upper right of screen.