DrAzzy:
What you usually do in a case like this is switch that dummy load with a MOSFET, and pulse it on briefly every time you wake up (and use the WDT to wake every 8 seconds for this purpose) - in the vast majority of things with autoshutoff, a brief pulse of the load periodically is enough to keep them awake.
Exactly. Post #6 and #9 here Powering the arduino nano with a Power bank - Project Guidance - Arduino Forum go in this direction, but it requires some experiment with the specific power bank to minimise the wasted energy.