As far as battery technology goes ... Luckily, [Paul] sent in a great tutorial on building a LiPo charger that works over USB. The board [Paul] came up with is incredibly small – just barely ...

In the first study, a team led by Professor Jong-sung Yu at the DGIST Department of Energy Science and Engineering developed a nitrogen-doped porous carbon material ...

But LiPo cells must not be charged in freezing ... the battery with an integrated heater and preheat the battery to a safe charging temperature as well. So, just like everything with electronics ...