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I have found that the battery life of DSLRs is often denoted in terms of possible shots rather than in running time (e.g. according to snapsort, one battery life on a EOS 70D is enough for 920 shots vs. 1100 shots on a 40D). This got me thinking as to what are the main sources of power/battery drainage on DSLRs (specifically, Canon EOS cameras), and what can in turn be done to increase battery life.

So:

  1. Apart from taking a picture, what are the functions/actions that drain the battery the most and how do those compare to the power reqired for taking a picture? (I'm especially interested in any setting/function that will have a significant impact on battery life; for example, the image stabilisation function on some ES-F lenses? Continuous focusing using AI Servo AF?)
  2. While I'm out taking pictures, is it 'worth it' to turn the camera off in between shots (assuming the intervals will rather be minutes/tens of minutes than hours)? Or is the power consumption while the camera is turned on but not taking pictures negligible?
  3. How big an impact does the LCD screen have on the battery life? I assume using the Liveview instead of the Viewfinder continuously will drain the battery faster. However I usually use the Viewfinder and have only the info display turned on (the one where I can access the quick settings). Does this drain the battery considerably as well (i.e. is it wort considering turning it off entirely)?
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LCD screen and any wireless features like Bluetooth, WiFi or GPS would be the heaviest drain. This would be followed by flash/focus-assist then auto-focus, image stabilization would probably be next. Just being on (or even off and providing enough power for the display counts) would be a minor drain. Keeping the camera on between shots won't do too much. IS/VR/OS and AF probably don't drain much as long as you aren't activating the camera's focus. But most dSLRs turn on really quick so if you are trying to get the most out of your battery just shut the camera off when you aren't taking a picture.

To save battery life don't use live preview or video features and turn off the show picture after every shot feature.

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    \$\begingroup\$ All in all it's really easier to keep a couple spare batteries on hand :-) \$\endgroup\$
    – Carl Witthoft
    Jun 13, 2016 at 17:24
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    \$\begingroup\$ @MatthewWhited - getting on site to find a dead battery is just poor planning. It's easily fixed, just charge the battery as soon as you get home. \$\endgroup\$
    – James Snell
    Jun 13, 2016 at 17:38
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    \$\begingroup\$ +1 to this. Most CPU's like the Fujitsu FRV and Arm used in DSLR's also scale the CPU clock and have 'idle' speeds, so features like facial recognition or video that require much more CPU and system activity will also put more load on the battery. But it is definitely easier to just have spares, or a grip that takes AA's for emergencies. \$\endgroup\$
    – James Snell
    Jun 13, 2016 at 17:41
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    \$\begingroup\$ @JamesSnell Li-ion batteries are not low self discharge like NiMH batteries are. Most manufacturers recommending recharging them just before use rather than just after use. If you shoot every day it's a moot point. But if you recharged them the last time you shot and then wait a month they won't be even close to full capacity, even if they haven't been in the camera (which usually puts a small load on batteries even when turned off). \$\endgroup\$
    – Michael C
    Jun 13, 2016 at 19:26
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    \$\begingroup\$ @MoritzLost That's a different question and should be asked as such. \$\endgroup\$
    – user
    Jun 14, 2016 at 9:23
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The number quoted is usually the one achieved according the the CIPA standard. This is a procedure where the camera takes a few shots, is power cycled between every group of shots and flash is used 50% of the time. As you speculate, not all actions drain the camera equally.

Based on experience of using hundreds of digital cameras of various brands, the main culprit is often the flash. You can easily get 50% more shots simply by not using the built-in flash. Cameras without one often have skewed battery-life numbers because those are measured without flash use. External flashes have their own power source in most cases, so they require only triggering voltage.

A built GPS is often a second source of high drain. Turning it off certainly allows many more shots to be taken since a GPS must always be active to keep position accurate for the next shot. With many GPS-equipped cameras, I have noticed at least 50% lower battery-life with the GPS on.

For non-GPS equipped cameras, the circuitry driving the display seems to be the second largest item draining battery. The more you review your images and the longer you do it for, the shorter the battery charge will last. While somewhat counter intuitive, it is the circuitry rather than the backlight which is more power hungry. You can notice this in cameras with both an LCD and EVF where the number of shots-per-charge is almost always quoted to be lower for EVF use than LCD use! Obviously, an EVF needs much less backlight than an LCD but the former often have a much higher resolution. Still, you can gain some battery-life by reducing the brightness of your displays and turning off automatic review.

WiFi usually turns off after a few seconds of inactivity, so it impacts battery-life much less. AF and IS obviously use some power but I've not seen either have a significant performance impact, perhaps if using a large lens with heavier/larger optical elements.

Certain software process occurring within the camera noticeably affect battery-life. Built-in HDR is a big one and some other processing such as optical corrections, noise-reduction and filter effects can all use up a non-trivial amount of power. Long-shutter noise-reduction also has a large impact when it is applied since it basically doubles exposure times.

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  • \$\begingroup\$ I'm a bit confused by the fourth paragraph, especially "Obviously, an EVF needs much less backlight than an EVF" Does an OVF even have a backlight? Wouldn't a higher resolution increase the complexity of the circuitry? \$\endgroup\$
    – Waddles
    Jun 14, 2016 at 6:09
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    \$\begingroup\$ @Waddles I think it meant to say "EVF needs much less backlight than an LCD" (meaning rear panel LCD). EVF has an eyecup while LCD needs to compete with daylight. \$\endgroup\$
    – hobbs
    Jun 14, 2016 at 6:28
  • \$\begingroup\$ @hobbs Oh, I see. I think it would be important to note that OVF use doesn't necesarily mean you're using the LCD. I generally have shot review disabled. Maybe change to "almost always quoted to be lower for EVF use than LCD use"? \$\endgroup\$
    – Waddles
    Jun 14, 2016 at 6:37
  • \$\begingroup\$ @Waddles well I think this answer is a little bit confused, especially where resolution comes into it, and where it seems to equate OVF with LCD usage, but what is true is that with EVF enabled, the camera is constantly (30 times per second, or so) pulling an image off of the sensor and processing it for display, while with OVF no such thing happens; and that image capture and processing is a substantial battery hog. Live view using the LCD would be just as bad. \$\endgroup\$
    – hobbs
    Jun 14, 2016 at 6:41
  • \$\begingroup\$ OVF has no backlight but when you have a mirrorless camera what you have is an EVF and LCD. The LCD needs a lot more brightness to be visible but ends up being less power hungry because it has less circuitry. Personally, I found this counter-intuitive. \$\endgroup\$
    – Itai
    Jun 14, 2016 at 16:24

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