My MacBook Air 13” 2017 shuts down unexpectedly when battery is more than half charged. Then indicates needs charging.

Also try running the Apple Diagnostics to see if any hardware issues are detected. Unfortunately the diagnostics don't detect all battery failures. In fact some battery failures can be difficult to detect or confirm. Most likely you do have a bad battery so you may want to have Apple or an Apple Authorized Service Provider examine the laptop since their service diagnostics may be able to better detect a battery failure (the service diagnostics also don't detect all failures, but they tend to detect a bit more than the standard consumer diagnostic). I would insist they also run the Cooling Diagnostic if the default MRI test they run does not reveal any issues (Apple doesn't like to run more than the MRI though), but the Cooling Diagnostic has on occasion detected a battery issue when the MRI did not.

Also make sure the laptop is not scheduled to shutdown.

An SMC Reset is justified for that problem: How to reset the SMC of your Mac - Apple Support.

I've done this SMC Reset and it actually made the problem worse. Now I'm only able to use the laptop when plugged in. Otherwise completely shuts down even though there is a charge on the battery.