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New Contributor
Posts: 1
Registered: ‎03-15-2016

Re: Cannot communicate with battery - 7D

This is a really useful thread, thanks for all the advice about taking apart the camera.

How will I know (or how can I test) if the loose screws have done any damage?

I've retrieved 2 loose screws (on the left as seen in the video, but also the one on the right) and I've still got a permanent "Error 40" message showing, despite the screws being back where they should be. The left one was very close to where it should have been, the right one I had to go a little deeper, and found it magnetically stuck to the cylindrical metal thing on that side.

Any help greatly appreciated!




Tom Quigley

New Contributor
Posts: 1
Registered: ‎12-28-2016

Re: Cannot communicate with battery - 7D

I had the battery communication error and tried the fix in the video. The screw on the left side (orientation per video) was very loose, but still in place. I put it all back together and still had the issue. 

Based on squiggly's comments, I took apart the camera again to find the 2nd screw (on the right side) loose in the body and 'magnetically stuck' as squiggly describes. I got the screw out and put it in the right-side hole, reassembled the bottom, reinstalled the battery. And this worked - no battery error. 


I never had the Error 40 but the comments about two screws out of position was helpful. 


New Contributor
Posts: 1
Registered: ‎01-19-2018

Re: Cannot communicate with battery - 7D

Here is my experience:  I dropped my EOS 7D into the hurricane Harvey flood, got home and tried to turn it on after several days with a different (i.e. dry) lens.  Nothing happened - the display on the back remained dark and the camera was silent.  I bought a new (second hand) 7D camera and tried the original lens and the lens did not autofocus.  Bought another lens.  I was able to use the flooded battery in the new camera and it worked fine.


After four months I put the original lens on the new camera, lo and behold, it evidently had dried out and it worked perfectly!


So now I tried to put the battery from the new camera into the original camera.  When I turned it on I got the "Cannot communicate with battery" error, but when I hit the "Cancel" button I was able to bring up the camera menu on the LCD.  However I am unable to take a photo.


In my case the problem is therefore with the camera, because I am able to use all three of my batteries in the new camera and none of them work in the old one.


At least the lens recovered from my stupid mistake (falling into the flood waters), but the camera shop still thinks the camera may not be worth repairing. I hope this info helps somebody.


Occasional Contributor
Posts: 10
Registered: ‎06-28-2014

Re: Cannot communicate with battery - 7D



I spent 10 weeks doing disaster response in Puerto Rico and St. Croix, I left my 7D's at home, brought a less expensive camera, unfortunately, the photos don't compare.


I used to have a company's name, found them on ebay, and they had lots of circuit boards and canon parts, don't know if they were new, pulls, etc.  Have you tried doing a complete reset of the camera, even removing the coin cell from the battery compartment?  Usually the problem I've found with batteries not working in a camera is that they are aftermarket batteries.  If it can not communicate, and you tell it to work anyway, usually the only problem is you can't see the battery gage, so in your case, I have to wonder if the battery was really charged, have you checked it with a meter?  Meters may not give true readings as they don't put a load on the battery, but if the voltage is low, then it's low, the false reading would be if it show full voltage with no load but once a load is applied, the voltage sags.


I've had the occasion to repair a canon lens or two, for a lens, there is a lot of electronics inside that lens barrel.  I took a lens all apart in a motel room on the bed, used my cell phone to document every step of the way so I could get it back together.  You were lucky that the water all evaporated and left no conductive deposits.


I was at Hurricane Katrina, with my canon power-shot, out doors took fine photos, once I got onboard the ship, a navy assault carrier, well air conditioned, moisture inside the camera would condense and killed the camera.  I had to ship it back to canon for repair. I've heard some people will put the cam in a sealed plastic bag, also having packets of silica gel helps.


I don't know if I'm helpful or not, if I can help though, let me know.



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