Joseph Griltz wrote:
We no longer retail the external battery packs for iFly. 
However, I would recommend purchasing this from amazon. It has the necessary power the iFly needs.
https://www.amazon.com/dp/B01G070FLA
 
 
I'm going to amend JJs recommendation:  First, this is more an option than a recommendation...we have one of these batteries in our office and it seems to work well.  A bit bulky, but has tons of power and versatility.  But our experience with the battery is not extensive.
Second, this battery pack no longer carries a tip compatible with the iFly.  So you will also need to get this collection of tips, which has one that fits: https://www.amazon.com/dp/B01C5F4GW0
-Walter