A battery of that size would need a lot of active cooling during charging. As this is a paper based battery the charge rate would have to be a lot lower to prevent hots pots. Not suggesting the paper is any more flammable just that the material is a better insulator and so will heat up.
Simple maths - it take 3 hours to charge the 7kwh Twizy battery and the paper battery would take charge at 50% of the Twizy assuming the same efficiency. !50KWh battery would take over 300 hours. Even at Twizy rates it would still take 2.5 days with no self discharge.
These batteries are really going to need some fancy charges - Tesla style super charges.