Troubleshooting my Macbook Air battery

[GanChan]

My 2013 Macbook Air is acting funny. Once the battery level dips below about 25 percent, the thing just shuts down. Sometimes it takes the time/date settings with it. I'm assuming the battery is just wearing out, but wondering whether anything else could be an issue -- maybe the machine is getting too hot, etc?

What would be the sensible troubleshooting routine for this unit?

I've tended to keep it plugged in with the battery at 100 percent much of the time. Maybe that reduced the battery life?

 

[Audit13]

You can check the battery health and cycle count using Coconut Flavor. At this point, the battery is several years old and is probably ready to be replaced.

 

[Fishrrman]

I'd take it to an Apple Store to see if they will still replace the battery.
Will cost about $200, but worth it if you plan keeping it a while longer.