If I power my project using a PowerBank only (without the wall connector), I wonder how long I can use it before need to recharge.
Say I get a fully charged 20000mAh power bank. The Arduino will power a 2 x 16 LCD (no backlight) and start a count down process from 2 minutes. Once 2 min is up, a stepper motor (also powered using the power bank) take consumes 200 mA would run for 10 sec, and that's the end of the program. I will put the Arduino to sleep after this, and I assume the power bank will shut itself off after awhile with minimal current draw.
Suppose the program runs once per day. A simplistic calculation shows that it would be years before I need to recharge the power bank. But I feel in reality it won't last nearly this long, is that correct? The battery will probably lose juice on its own and I might've overlooked some other sources of loss?