Type-c 18650 3.7V 2500mAh Li-ion Rechargeable Battery Indicator Power bank battery Mobile charging battery - AliExpress
Lithium Ion Cylindrical Battery - 3.7v 2200mAh : ID 1781 : $9.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Amazon.com: ICR10440 Lithium Ion Rechargeable Battery 3.7V 350mAh with USB Charger (2pc Button top +Charger)(They are not AA Size Battery) : Health & Household