battery

How old is the computer?

For details about your Mac model, click the Apple  icon at the top left of your screen and choose About This Mac.

This is likely just a normal message from the OS as it determines that your battery can't work as well as it used to. It's likely that this is a normal symptom of an aging battery. You can continue to use the machine until you can replace the battery.

However, if there is any indication that the battery may be swelling or bulging, maybe a slight bow in the top or bottom of the laptop, then stop using the laptop and have the battery replaced by an Apple Authorized Service Provider immediately.

If the indicator states that it needs service or needs to be replaced, you can have that done at the Apple Store, or at an independent Apple Authorized Service Provider. I went to the latter, because the laptop in question was a 2013 Macbook Air, now considered "obsolete" by Apple which means Apple no longer stocks the parts for it or does repairs on it. The service shop I used had me order the battery myself from OWC and bring it in, they replaced my old battery for about $25 for the labor, in less than one hour. Some people are comfortable replacing the battery themselves (I was not one of those), the new battery comes with all the tools (mostly screwdrivers for the tiny laptop screws) and instructions for how to do this yourself if you are so inclined.

If your laptop is newer, the Apple Store can handle this for you right there as well.