Amazon.com: PKCELL ICR10440 Lithium Ion Rechargeable Battery 3.7V 350mAh with USB Charger (2pc Button top +Charger)(They are not AA Size Battery) : Health & Household
Lithium Ion Cylindrical Battery - 3.7v 2200mAh : ID 1781 : $9.95 : Adafruit Industries, Unique & fun DIY electronics and kits
4/3 A 3.7 Volt Lithium Ion 18500 Battery (1600 mAh) - Only Batteries
All you need to know about the 3.7V lithium ion battery-Tycorun Batteries