I'm talking about proprietary batteries that require a special charger. If you are on a ten day trek you are screwed short of bringing few extras with you but than again you are still not 100% covered. I like new solutions where you can charge things thru usb (in my case solar power), remove the battery and bring extra or if needed replace it with AAs. That makes it very usueful tool while trekking. I can't wait for digital cameras to be entered into that equation as well.