Here you need the NB Battery plugged into the NB to charge it. More than slightly difficult to switch over so they charge the spare batteries when you are asleep and no where near enough time for a full charge when you wake up in the morning have a shave, shower and whatever that third s word is and breakfast.

I suppose you could of course carry 2 NB's and use the second one to charge the spare battery for your first NB but that seems rather expensive not to mention Excess Baggage prices.

Col