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Maximizing Canon EOS Battery Life

Canon makes some really awesome DSLR cameras. What they don't do is tell you how to get the most out of your batteries. Sure, there are general rules like turn the camera off when not in use, don't chimp more than you have to - but to the best of my knowledge, to date nobody has actually quantified how much some of these items really cost.

Until now!

This all started because a recently acquired camera (Canon EOS 50D) seemed to eat batteries for breakfast, lunch, and dinner. My first thought was this might be a recurrence of a problem I'd previously had with my first EOS 650. So I recreated the same tool I'd done back in 1987 only for the new DSLRs, and took measurements. My goal is to translate Electrical Engineer-Speak into some real world numbers that anyone can understand. 

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How manufacturing tolerances can screw you!

Back in 1987 I bought my first 35mm SLR - an EOS 650, with the 35-70 f/3.5-4.5 and 70-210 f/4 zoom lenses. I shopped around the various vendors in the back of Popular Photography and eventually brought that info to a local camera store and basically said I didn't expect to meet the price, but did value a local contact should there be any issues and expect if he wanted the business to see what he could do about discounting off list price.

The owner, a man looking like he was in his 60s, came down somewhat - not to where mail order was but enough that I felt it was a win-win, so made the purchase. About 3 months later I exhausted my first $20 battery - a 2CR5 and quickly popped in another. Within a week, that one was drained.

After spending $100 in batteries, my spidee sense told me something was seriously wrong with my equipment. So I split one battery apart, removed the cells, and attached small wires to the inside. Bringing those wires out of the camera and soldering wires to a couple of nails and a rubber band, I was able to make a brand new 2CR5 battery as an external battery where I could now insert a current meter to see just how much juice the camera was taking.

Taking lots of measurements and cutting to the chase ...

When I left the 70-210mm lens mounted to the camera, the current consumption of the camera / lens combination was about 1000x higher when powered off than it was when the 35-70mm lens was attached or if no lens was attached! It was as if the 70-210mm lens was preventing the camera from turning fully off, though there was no indication in the camera itself that it wasn't turned off. So if I left the 70-210 on the camera powered off and in the camera bag, in a day or two my battery was totally dead.

I brought the entire setup to the camera store. Described what was happening and asked if I could first demonstrate then use some of his demo stock to isolate the problem. I didn't know if I had a problem with the camera or with the lens. He agreed. All setup, demonstrated, then I took a couple of different 70-210 lenses and when connected to my camera all went down to a couple of micro-amp draw instead of milliamp draws when powered off just like the 35-70 did. Then I tried a couple of different EOS 650 bodies. When connected to my lens, none of those bodies with my lens exhibited the problem.

The problem was only apparent with my lens and my camera body!  

The owner wanted me to send it to Canon for warranty work, and in the end he exchanged it in the store - which was why I wanted a local face to buy from. I just couldn't imagine Canon setting everything up the way I had to see the problem firsthand and thus be able to diagnose / repair it.  

What was likely happening

Everything is built to a certain specification, and that spec has an error margin on every measurement. This is true for everything - the tiles on your floor, the wood 2x4s that are in the walls of your house, the batteries that power your equipment, every electrical component in everything electrical, etc. Those errors can sometimes align themselves in opposite directions and have interesting consequences.

In my case, something about either the electrical connections or the data timing between the lens and camera were likely causing something in the camera to think it needed to keep applying power to the lens, and thus my combination was eating batteries for breakfast.

So that is my camera / tolerance story...

David Soussan