What can I do to slow down battery degradation of portable power bank for my Android phone?

I just got Inland USB-A 5,200mAh Power Bank w/ LED Indicators for my android phone. It has a one-year warrantee, which seems to tell that its battery might degrade significantly after one year of uses.

The power bank came fully charged. I don’t have a plan of using it sometime soon, except for something unexpectedly. and will just set it aside for weeks or even months. I was wondering how to slow down battery degradation as much as possible?
For example:

  • In what percentage of charge shall I leave it, when I set it aside? Emptily, fully charged, or somewhere between?

  • Does its battery degradation depend on how many times it has been discharged and then charged, and how often it has been ?