1) I use my laptop almost exclusively at home or in other locations with a wall outlet available. If I needed to take it out and about for a day or week and was worried about running out of juice, I might consider renting a battery pack instead of buying one to sit in the closet and eventually explode.

2) if I were traveling overseas and didn’t want to schlep heavy battery packs for phone, tablet, etc. I’d consider renting them for the duration of my stay.

3) I’m out and about and not only has my phone’s battery run down, but so has my external battery pack (or maybe I forgot it at home). If rentals were available at every bodega; as easy to rent as it is to pop in and buy a bottle of water; and as easy to return as a library book, that might be an option.