The theory is that it can be charged, but what you have to consider is that the mobile phone charges the charging bank: First, the charging bank itself takes about ten hours or even longer.
Secondly, it is necessary to consider the transfer of mobile phone power to the charging bank, and how much electricity can be converted. That is to say, 100 percent of the phone's power is transferred to the charging bank, and it is possible that only 50 percent of the power is transferred to the charging bank. And this 50% of the electricity may only be equivalent to the charging bank on the socket for half an hour.
We assume that the charging bank takes ten hours to be fully charged, then half an hour is equivalent to five percent of the power of the charging bank, then you tell me the phone charging value for the charging bank?
The result can only be that the charging bank is also out of power, and the phone is also out of power. There is an important factor here, that is, a part of the power can not be converted when charging.