I am trying to find a very portable way to power a nema 17 1.2A bipolar stepper motor. I was looking at the Anker 20100 power bank (https://www.amazon.com/Portable-Cha...C_SX236_SY340_QL65&keywords=anker+20100&psc=1)
And it seems to have everything i need but my worry is that it will be like most power banks and not live up to its ratings and i cant find any videos in English of someone testing it at max current draw.

I had a power bank rated for 1A output and i tried to draw that much from it with my nema 11 stepper motor and the over current protection kicked in and shut it down so my guess is that the anker 20100 wont be any different.

I looked around and found out that 18650 cells have some that can output up to 10A. So i looked for how to properly turn them into a decent battery pack and found a LOT of cheap easy boards that do just that but then their output limits are always 2.1A leaving me with not enough current to power my stepper because 1.2A on a 2 phase motor means it needs 2.4A to work properly.

So i looked again and found some BMS boards that use 3 cells in series and allow an output of up to 10A but they have no convenient way to then recharge the cells like the other boards.

I know power tool batteries have some monster current but cant seem to find any that arent around the size of 2 bricks glued together.

 

Have a look for some of the chargers used for RC models. They have cell balancing chargers.

 

For the Anker you can just buy it and then test the current capacity, if it does not give you the advertised current then you can return it, with evidences I believe they will gave you full refund. But if it were me then I would hack the board to give 2.4A. Look up the datasheet of the power IC and check if it can handle more than 2.4A, it most likely will. They will likely insert a current sense resistor to monitor the current, you use the formula provided in the datasheet to calculate the required resistance for 2.4A, then replace the current sense resistor to that value you calculated. But make sure that IC cooling is sufficient (get bigger heatsink), or you will brew it up!
If the IC can't handle more than 2.4A then you must find another solution, maybe just need to search more deeply.