Many power banks have to be returned because they don't meet the specs they published. That is, your bank claims 30K mAh but is it? Either you are using what power it has quickly or it's not really 30K. Testing would require some gear.
I have spass k6 30000mAh power bank. When I charge my phone, power bank is draining fast. This power bank ask input of 5V/2A current. Normally I am charging the power bank with my mobile phone charger adapter which is having 5V/1A output. Is that the problem for that fast draining issue.? Thank you