How to calculate the required capacity of a powerbank?

Question

Electronics

There is a device that consumes 1.4 amps at 5 volts. Continuous work for 5-6 hours is required.
For food, I plan to buy an empty powerbank + 18650 with a capacity of 2000. How many cans will I need? Something got mixed up in the calculations.

Answer 1

Rough energy calculation.
In total, 1.4 A * 5 V * 6 h = 42 VAh of energy will be required. One bank can provide 3.7 V * 2 Ah = 7.4 WAh. I believe that six cans are enough, without taking into account the degradation of elements, current load and the efficiency of the DC-DC converter (if used).