Diagram for help

Capitor

Gotta be little more specific. Power bank...for what?

If you wanna charge your phone you'd need 5V/1A i presume. There are a few options here. If you wanna charge it with a standard 5V input things tend to get hard. Then you charge 3.7V battery and need to step it up to 5V. These circuit's vary in complexity from medium to hard. This brings me to my second preposition. The much simpler topology is 2x3,7V batteries in series to add up to 7.4V. Then it's just a simple matter of stepping it down with a zener or something. But then you won't be able to recharge the bank with 5V but with ~8V. Simply put the advantage of stepping up the voltage is you'll be able to recharge the bank with 5V. The disadvantage is very complex circuit mixture of transformers analog digital circuitry. If you're a beginner i don't suggest going there. Your second option has the advantage of simplicity and compactness but will require a non standard recharging adapter. Either way you should be searching for 3.7V to 5V circuit (i assume that's the capacity of your bank's battery and the required output)

I think a its a 55 v a I presume

Please look up for my circuit related to power bank. I just dinished it with LM317 for single cell 3.7v lithium ion. I am working on next IC as well. Please look up for it and find it with my published name. Thank you :)