Apex Batteries

Stefan don’t get confused by the CR123, CR123A, R123, R123A, RCR123, or RCR123A. They can even be called 16340 referring to their dimensions in mm. These are all essentially the same type of battery. The non rechargeable lithium primary cells are 3v where as lithium ion rechargeable are generally 3.7v. The mAH is referring to capacity so more is better. Actual mAH is often much different than advertised. Your Apex Pro specifies 3v non rechargeables however several people at candlepowerforums report no issues running 3.7v lithium ion. Many LED lights like this will have a circuit allowing for different voltage inputs. If it were me I would go ahead and use 3.7v lithium ion cells. If you are concerned there are several 3.0v rechargeable lithium ion and LiFePO4 cells around. Battery Junction has several good choices. I have had good luck with these batteries and this charger for my flashlight.

Thanks so much, very informative. I think i saw another thread here that said the Apex could handle 8.4 total volts because its regulated, so hopefully two 3.7s will work if they are consistant. I was suspicious of the mAh ratings, because ive seen a range of 800 to 1800, and i dont see how thats possible. Anyways, ill go ahead and order the ones you recommended….worst case scenario, gotta love REI return policy. :)
Still, if anybody has any experience with this particular headlamp, ide love to hear about it.

I don't have much to add since I have the regular Apex and not the Pro, but I will say that rechargables are a very good idea because the Apex chugs battery power and get the best ones you can because it's a lot lighter to carry four 1800mAh batteries than 8 900 mAh ones.