The battery you need for the Freeflight Moto 18650 Battery Extension Tube is:
(Amount=3) – INR18650-25R 2500mAh Flat Top Battery ( It needs to be exactly the 18650 2500MAH Flat Top )
https://www.amazon.com/Samsung-INR18650-25R-2500mAh-Rechargeable-Batteries/dp/B00NUI4AAU/ref=sr_1_11?ie=UTF8&qid=1470154142&sr=8-11&keywords=18650+2500MAHINR18650-25R-datasheet
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