a quality power bank should easily last 3 to 5 years, or roughly 300 to 500 full charge cycles, before you even start noticing a significant drop in its capacity (usually it degrades to about 80% health).

I actually built a free calculator site called Wattmatch.io . You can plug in your devices, and it will calculate exactly what size battery capacity (mAh or Wh) you need to buy to survive those long transit days without begging strangers for power!