you can but you dont gain much because they run concurrent since both are at 9 volts and aa's cost more in the long run. So i would leave empty or pick up the 4 d pack for the camera and replace the aa pack, that way it will run on the external first then switch to the internals when they die. you will also see this on your report. The 4 pack will pay for it self in a year since you will save money , time and gas when running that set up with D's. This is why by 2021 we will be only shipping units with 4 d internal batteries and the boosters will be 6 d. This will be much easier for consumers to understand and the performance is better as well.