Waterproof 3xAA Battery Holder with On/Off Switch : ID 771 : $3.95 : Adafruit Industries, Unique & fun DIY electronics and kits
5.11 Tactical Waterproof Battery Case - Walmart.com
Amazon.co.jp: 3 AA Batteries 4.5 V Battery Box, Waterproof, Switch Included, Easy Open and Close Lock Type, 3 x AA Batteries, 4.5 V, Battery Holder, AA Battery, Waterproof Battery Case, 2 Wires :
Scurion - Battery case 'Speleo'
LifeProof Announces First Waterproof Battery Case for Plus-Sized iPhones