How to tell if Anker Powercore 20100+ is fully charged?

Is powercore+ 20100 not the model number?

hello, I was also wondering, is it important to charge with a specified charger ? or any mobile charger is ok ? Thank you for your help.

Sorry again, I have the 26000 and it seems that I cannot use it to charge a mobile when the powerbank is charging ? I could do it with my former very cheap powerbanks, but not with expensive Anker ? can you confirm please ? thank you.

These don’t support passthru.

Sorry, it means that all Anker cannot be used when charging ?
isn’t it too stupid ?