I`ve found something else that would work :-)
The Chinese company I import the E-cigs from also sells all sorts of electronic stuff (check them out and I`ve posted a link to what I`m on about .....
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I`ve already got loads of 18650 Li-ion batteries ranging from 2000mah to 2950mah for various applications.
Two of these in this powerpack would give me 4000-5900mah.
Assuming the 950mah Binatone battery gives 2hrs then I should have from 8-11hrs of backup use :-)
Output of this pack (with batteries fitted) is 5v at 1.0ah the same as the mains charger I use :-)