This is a write-up for a quick battery life test I did with the Rebel XT + Opteka BGRXT. Note: this is the exact same grip as the Canon BG-E3.
The issue:
I’ve read in a number of online forums that the Rebel XT does not function well with NiMH installed in the (optional) BG-E3 grip. The stated reason being the NiMH batteries have a voltage of only 1.2V compared to 1.5V for alkaline cells.
The grip may have either 1 x NB-2LH, 2 x NB-2LH (in parallel, not series), or 6 x AA cells installed in it. The NB-2LH battery from Canon is rated at 7.4V/720mAh. So you can see immediately that even with 6 AA NiMH batteries only 7.2V is being supplied to the camera. Supposedly this is very close to the voltage that a NB-2LH battery supplies when it is almost exhausted so this is also the triggering voltage from the Rebel XT shut itself down.
My only personal experience with this experience is that my Rebel XT with 6 x AA 2500mAh batteries fresh out of the box (factory charge only) shut itself down after somewhere between 20 and 30 exposures.
Test setup:
Canon Rebel XT with firmware v1.03 with EF 50mm f/1.4 attached. 6 x AA Maha 2500mAh NiMH AA batteries (lot# 0 5-10 SR). The batteries had never before been used and were fully changed immediately before the test in a Maha 1-hour charger (model #MH-C801D) set to the use the 2-hour ‘soft’ charge cycle. The batteries were then allowed to completely cool for ~2 hours prior to use. After battery installation the camera was switched on to verify that the batteries were properly seated. The battery status on the LCD displayed showed 3 of 3 bars. AF was tested on various object in my living room and the flash was fired once (FEL button). The camera seemed to be operating normally. The camera was then switched off and a 2 GB SanDisk Extreme III card was installed. When the camera was switched on again the LCD battery status showed 1 of 3 bars. The TFT LCD was used briefly to format the card. The camera was (some what randomly) set to mode M, 1/25s, f/2.8, AF mode “AI focus”, drive mode was set to continuous shooting.
The test:
The camera was pointed at a white wall (to reduce image file size) and the shutter release held down. Two brief pauses (~30s) were made in the first 979 exposures, taken in order to give the shutter a rest period. It was then noticed that a small spot on the back of the body felt slightly warm to the touch. This could have been heat transferred from my hands or internal heat from the camera. The camera was switched off and given approximately a 1 hour period to cool down just in case this was shutter mechanism heating up. The camera was switched on again at the setting were changed to M, 1/6s, f/1.4, manual focus to reduce any unnecessary wear and tear. Another brief pause was taken during this second exposure cycle. The CF card filled up at a total of 1297 exposures. It was decided to terminate the test at this point to prevent any further wear and tear on the shutter mechanism. The LCD battery status still showed the battery at 1 of 3 bars. It did sound like the shutter firing rate slowed down slightly during the second exposure cycle. I attempted to confirm this but looking at the file creation times of each JPEG (find . -type f | xargs ls -la –full-time | awk ‘{print $7}’) but they were written to disk in a somewhat bursty manner. E.g.:
16:54:16.000000000
16:54:16.000000000
16:54:16.000000000
16:54:16.000000000
16:54:18.000000000
16:54:18.000000000
16:54:18.000000000
16:54:18.000000000
16:54:20.000000000
16:54:20.000000000
16:54:20.000000000
16:54:20.000000000
A cursory inspection with ‘exiftool’ shows the that frame rate was close 2FPS towards the end of the test. Further testing is required to determine if this was the result of the battery voltage drooping of change of the shutter speed to 1/6s. The EXIF data will be saved for later analysis.
Summary:
It appears that Rebel XT would be usable in ‘the field” with AA 2500mAh (1.2v) NiHM AA batteries. From this test it is not possible to conclude if this is only the case with brand new batteries under an ideal handling situation or if the voltage output of the particular model of battery used will be stable enough in the general case to prevent the camera from shutting down.
Future work:
No means of testing the voltage output of the batteries under load before/after the test was available. It would be interesting to compare the behavior of AA NiHM batteries vs. a NB-2LH battery.
Note to other potential testers:
In retrospect I should have started the test with the lens in manual focus, the shutter speed set to 1/6s (twice the max FPS exposure rate of this camera), and the aperture wide open. This would be to reduce the wear and tear on the shutter and lenses diaphragm. I also should have changed the image quality settings to ‘Small Normal’ and leave the lens cap on to further reduce the size of the image files.
Update:
I also posted this write-up to the dpreview.com Canon EOS 300D/350D forum.