Battery sharing

We were at a family event last night and all three of my kids had the battery die on their phone before the event ended. I had over 80% battery on my phone. What I wished I could do was easily give them some of my battery to get them through the night.

I had this image in my mind of holding the backs of two iPhones together and hitting a button and having the one with lots of battery give some of it to the one that was running out.

Even if such a thing required connecting the two phones with a cord, it would be pretty great.

I'm wondering why this isn't possible, particularly the connecting two phones with a cord and having one give some of its battery power to the other. I'm sure there is someone out there much smarter than I am about battery technology who can answer this question.

Of all the great things that Apple and the Android phone companies have brought to the market over the years, the one thing that still sucks about smartphones is battery life. And with billions of people walking around with these devices in their pockets, it seems that tapping into all of that excess battery power to give a dying phone some extra life would be an incredible feature. It can't be that they haven't considered it. It has to be that its not easy to do. But I'm not sure why.