How do you check the battery health of a power bank?

Is there a way to test the battery capacity? I have a couple Anker power banks, PowerCore 500 and 337/PowerCore 26K. Both are about 7 years old and been used very intermittently. I'm assuming the capacity has diminished with age, but want to get a better idea of how much since hoping to use them on an upcoming trip. The light indicator on both shows full though I can't recall the last time I charged them.

I'd also like to troubleshoot an Anker A1501 Jump Starter Portable Charger, which is about 8 years old. Noticed it seemingly stopped working 2-3 years ago. When plugged in it'll show as charging, but doesn't do anything if try to use the built-in flashlight or charging ports. Never used the feature to jump start a car.