3 x AAA Battery Holder with On/Off Switch and 2-Pin JST : ID 727 : $1.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Amazon.com: Duracell Coppertop AAA Batteries with Power Boost Ingredients, 24 Count Pack Triple A Battery with Long-Lasting Power, Alkaline AAA Battery for Household and Office Devices : Health & Household