Battery capacity and runtime calculation?

Question

Electronics

How to correctly calculate the operating time of the microcontroller (5v) from the battery? Judging by the multimeter, the converter 12-> 5v + the microcontroller itself consumes 7 milliamps. 7 Amp/hour battery from UPS. Or let's say for a power bank for 2000 milliamps at 5 volts when consuming 3 milliamps.

Answer 1

7Ah/0.007A = 1000h ≈ 41days.
We must also take into account the self-discharge current of the battery, lead-acid ones lose ~ 5% of the charge per month, which means a maximum of 38 days if there are no other losses.