Copied from the Chucklehead Forum...
The question of "What batteries do I get" and "Where do I order" comes up about a hundred times a week on the 'Saturday' thread.  I just want to put as much batt info as I can here so that we can point ppl to this thread when the question comes up. 
 
Here is a rundown of batteries that can be used for the Chuck....
 
 Large Chuck:
3.7V  - 18650
6V - 2x  RCR123
6V - 2x  CR2 (need the sleeve sold at Thagbuilt.com, 
unprotected**)
6V - 2x CR123 (these are non re-chargeables that you can get in a pinch at most stores to use your large chuck at 6V) 
 
 
Little Chuck:
3.7V  - 16340 (also sold as 3.6V CR123A, but make sure you get the 3.6V and not the 3V)
3.7V  - 18350 (1200mAh, orange ones 
unprotected**, blue ones protected)
 
 
** Use unprotected batteries at your own risk. While it is unlikely that anything will go wrong, serious injury and fire can result from using unprotected batteries. **
 
 
 Places to Buy:
 Look through the thread below for useful discount codes!
 
MadVapes
 
MadVapes LLC
 (US Supplier, good prices, carries protected 18350's)
Battery Junction 
 
BatteryJunction.com Batteries, Battery Chargers, Flashlights, Solar Products & more! (US supplier usually 2-3 days to get)
 
Lighthound
 
Fenix Flashlights, Cree Q5 LED, Lithium Batteries, Lithium Ion Batteries, Li-Ion Chargers, Leatherman Multitools, Spyderco Knives and more! (US Supplier, good prices)
 
Dealextreme
 
DealExtreme: Cool Gadgets at the Right Price - Site-Wide Free Shipping (Page 1) (China supplier, best prices, but extremely long wait)
 
 
Battery Tips:
- Order your batteries and charger at the same time you order your Chuck, so you won't be stuck looking at an unusable piece of table art. ;-)
 
- You can charge your batteries when they come. Don't wait for your Chuck to arrive. They will hold the charge and be ready for out of the box Chucking!