External Portable Battery Pack for MPC X or any MPC.

When you buy an AC powerbank, you add extra weight, plus you have to carry the power supply with you.
In addition, AC-DC conversion is simply a loss of power. You convert DC to AC and then back to DC.
And the MPC One, for example, draws a maximum of 20W under load:
viewtopic.php?f=48&t=211295&hilit=mpc+one+battery&start=15#p1845959