They are sub-C. I'm not exactly sure what that is. They are 1.2V 4Ah batteries. They say 4000mAh, but everywhere I've read say you divide by 1000 with mA and you get amps. The best designed DIY headlight was made of PVC. I went to the local hardware store and spent about 45 minutes looking at piping. None would come close to the correct type of material that I liked. Then I got onto Home Depot's website and found the light. I figured that if I could find a pre-assembled something it would hold out better. I'll try and take some pictures once I'm done.