Did it come with a cord? I suspect a USB cord. But mine has a 12v battery.
Hinge that thing and then bolt it to the bed. You could lay down or stand up to sleep..... 
The foot warmer plugs straight into the live mains so no worries about having to recharge it..

The small oval box in the pic is its controller, you can set it to Low/Med/High heat.
The only thing I don't like is that the bloody thing switches itself off after about 90 minutes as a "safety feature" (whatever that's supposed to mean) according to the instruction leaflet.
There's not even a ping to tell you its switched off, so you could be sitting there with your feet toasting nicely in it as you watch The Waltons on TV, then after about 90 mins your feet begin getting cold because it's switched itself off, and you have to bend down to switch it back on, grrr..
Speaking of the Waltons, I see the blurb for tonights forthcoming episode is "Granma feels she is being edged out of her position as church organist, so the family rally round to give her moral support."
Hmm sounds good..