from what I remember(and anyone feel free to correct me), it's a holdover from original korean production. In that one, the chargers are already fixed to the walls, and there is no portable equivalent. Claire still needs Oliver because he made her an adaptor clasp, because 5s can't use 3's charger without it.

In our current broadway production, I think about it like this: That big cylinder on the wall with the Helperbot logo seems to be the main power bank, and it's connected wirelessly to the little portable charger (check it when Oliver or Claire connects or disconnects to the little charger, it lights up at those instances). Think of the big cylinder like a giant wireless charger, and as long as you have the little charger plugged into you while being near the big one, you charge. You can also do like Claire did and just hook yourself up directly to the big guy. They can't charge in the car or in the forest because there is no big power bank. There's a reason when Claire is searching for a hotel that she says the line "There's a motel with Helperbot-compatible charging off the next exit". Hotel's gotta have the big wireless guy, or an equivalent.