Charging through an USB port is only possible at one side of the USB connection, not on both sides. Basically, the USB ports on a laptop are used to send a signal out, thus they can be used to power up something. Many rechargable USB devices are designed to get a signal in, thus they are waiting until they receive power through the port. Technically, this is all just a one-direction street.
Still, they could make a laptop that can be recharged through the USB port, if they add a receiving end to it. Basically, that would mean that you can't connect a device to your laptop, but you would be connecting your laptop, as if it's just another device, to another PC. Would this be practical? Maybe if you want to do this to set up a special network or whatever but no one has seen some true value in such a setup. Basically, you'd be downgrading your laptop to a portable hard disk.
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