Emergency charging for the RX100

My neighbor is going on vacation, and one of their cameras will be the RX100. However, they have been unable to buy a spare Sony NP-BX1 battery, and they are quite concerned about running out of power part way through the day.

They can buy an off-brand battery. I will mention that to them, but I don't know how they feel about it.

I heard that in an emergency, it is possible to charge the RX100 battery using AA cells. Does anyone have more information on this type of device?