I have 3 of the Moultrie Game Spy D55-IR trail cameras which require 6 each "C" batteries. I have been doing some testing using rechargeable batteries as follows:
1) Energizer 2500mAh listed at 1.2 volt. Out of the package I have found they vary from 1.2 to 1.28 volt. Charging them they will reach up to 1.44 volt and stabilize out around 1.39 volt. Installing them in the above camera, they show 75 to 78%. These batteries are a slow drain.
2) Pure Energy out of the package show 1.55 volt. Charging them, some will stabilize out at 1.60 volt. Installing them in the above camera they show 100%.
***Now for the problems:
1) Pure Energy are a shade longer than standard battery length. Multiply that by 3 as you are stacking 3 each poor side in the camera. This results in a very, very hard installation due to the extra total length.
2) Pure Energy batteries also have a larger center post (positive end). This post will not fit in the groove designed for it in the camera. Out comes the hobby knife to shave a little out of the camera to widen the groove.
3) To shorten the spring at the battery negative end, the camera has to be totally gutted being sure not to: remove the center 2 screws on the circuit board. This holds the IR pendulum. The silver screws come in various lengths and sizes, all near the same diameter.
The bottom of the top circuit board has pins near the center area that face downward and fit tight into a socket.
4) To make things interesting, there is also another ciruit board in the back of the camera. This also has to be carefully removed.
5) All the wiring is very fine.
Upon reassembly, extreme care has to be taken to make sure: 1)the wiring doesn't get damaged, 2) the pins on the circuit board do not get bent, 3) the on-off slide switch must be in the off position. Before putting in the top circuit board screws, make sure this switch is operating properly.
**Screw up on your spring modification (dismantling or reassembling) and your camera is useless.