No they can’t.
For that, you need a charger.
Anyway, here’s a pretty cool and science-y one called JuiceBee, a tiny, locally created black box that combines a cell phone charger and a backup battery into one. It’s good for camping and stuff. And it’s available for preorder now.
If you understand the basic concepts behind Legos and the Boy Scouts motto, then congratulations. You understand this thing. And if you don’t understand those concepts, the Boy Scouts motto is “Be Prepared” and Legos are colorful interlocking bricks that are fun for all ages.
Point is: it’s two pieces (a charger and a backup battery) that fit perfectly together as one and then keep your phone from dying in perilous situations. Use it like any normal charger. Plug it in overnight, wake up, have conversations. You won’t even notice that it also charged the backup battery while you slept.
At least not until you find yourself in a dicey, sans-walls camping situation and remember that you have a pre-charged battery with a built-in flashlight. Right. It’s also got a built-in flashlight.