EOS M: Hot-swappable DIY battery grip.

Started by Walter Schulz, April 23, 2021, 09:02:19 PM

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Another project you just added to my list , funny that I just received my 2nd eos m thanks Walter


I built a much easier external power solution for my EOS-M.  Just connected two 18650 cells in series and used the case of an old damaged LP-E6 battery to build a dummy battery.  I took the old cells out of it and used the original board inside the battery to connect the external Li-ion 18650 pack to the points where the old cells were originally connected.  In this way, the camera thinks that the original battery is connected and battery indicator, short circuit and overheating protection work just fine.  For the electrical connection to the external 18650 pack I used a 30 cm long cable that goes through the battery door lid on the bottom of the M inside the dummy battery and a male/female dc connector soldered to the dc output of the battery pack which makes it convenient to charge and disconnect.  The whole thing weighs 100 grams and I attach it to the horizontal arm of my gimbal using a rubber band as the ones girls use for their hair.  I plan to build also a battery holder plate with a screw to firmly attach the pack to the flash hotshoe of the camera in case I don't use the gimbal but film just hand held.  I wiil also build a second battery pack for long travel filming.

Since the EOS-M draws only between 390 and 420 mA of current (mode dependent) when recording video with ML, the above pack lasts forever.  I tested it for filling up a 64 GB card 10 times consecutively with anamorphic footage, (about 16 minutes at 1736x2928/10bits lossless/16 fps/continuous recording untill card is full) and there was still some power left.  The good thing about it is that the camera shuts down when the battery discharge voltage reaches about 6,5 V, thus protecting the batteries from a deep discharge that could damage them.   

Charging is very simple too.  I charge the pack from an adjustable constant voltage source set at 8,3 V, (the limit of 8,4V should not be exceeded).  It has a built in current limiter that does not allow the charge current to exceed 2A.  In that way the charge time is about two hours and you are ready to film ML video a whole day long.  Since the voltage difference between the two 18650 cells was less than 50 mV when fully charged, balancing was not necessary.

I have been using the above battery pack for over a year now and have been very satisfied by its performance.  It works and works and works and I haven't noticed any performance degradation so far. Highly recommended!

Here is the data sheet of the 18650 batteries that I bought for 4 Euros each at a local battery store:



If you decide to build the above battery pack by yourself, be careful NOT to short circuit the battery terminals.  Li-ion batteries have extremely low internal resistance and a permanent short circuit may cause fire!  I haven't tested that but what I did was to connect the dc connector to the battery terminals via a short Cu wire of 0,3 mm diameter which serves as a fuse.  In case of a short circuit, it burns out momentarily protecting the batteries from overheating.


Wow that grip looks so nice!
Would love to have one that doesn't require drilling a hole!
Ideally I would like the following adjustments:
1. it can use a dc in to a dummy battery
2. led light indicators instead of an oled panel
3. a usb-c charging port
4. Combo Arca swiss & manfrotto Quick Release Plate
5. 1/4" Tripod Screw Mount

sosad I do not have the skills and a 3d printer for this dream battery grip.