Adafruit 8 x AA battery holder with 5.5mm/2.1mm Plug and On/Off Switch
Make a portable power brick with plenty of juice! Use Alkaline AA's for a 12V 3000-4000mAh power supply, or rechargeable NiMH for 2000mAh 9.6V supply. Either one is good for running electronics that have a 5V voltage regulator (thus requiring a 7V+ supply) or perhaps some motors or solenoids.
Perfect for portable Arduinos, motors, solenoids, 12V LED strips, etc. An On/Off switch lets you control the power right at the source without unplugging. Batteries not included, may or may not include screws.