Does using EVF only, keeping the screen permanently switched off, increase battery life?

Question

I have found that when I have an electronic viewfinder, I don't use the screen. On my Powershot G5X with a rotating screen, I kept the screen permanently closed, using only the electronic viewfinder. I imagine not using the screen should increase battery life. However, if I require a rotating screen that strongly limits the available models for my next camera. Is it true that using only the electronic viewfinder, with the screen switched off, substantially (>20%) increases battery life?

I have specifically mirrorless cameras in mind. That may mean the answer is different than for DSLR.

(If yes, I will next ask a question whether there is a way to keep the screen permanently switched off on models without a rotating screen.)

Answer 1

Modern EVFs use more power than the LCD. Despite being much smaller, it is the circuitry that takes the most power. With typical LCDs having around 1 megapixel but many EVFs having 2.4 MP now (or up to 3.6 MP even!), power consumption is higher when using the EVF than the LCD. To answer your question then:

No. Using the EVF over the LCD usually does not improve battery life. In fact, it makes it worse. If you look up online battery-life for cameras with an EVF, you will notice lower numbers quoted when the EVF is used than the LCD.

In the case of your G5X specifically, you do save a bit by using the EVF. Canon quotes 210 vs 215. On the Sony A9 though, it is 480 with the EVF vs 650 with the LCD. Although some manufacturers do not quote separate numbers for battery-life with each, the majority that do show lower battery-life with the EVF than the LCD.

What saves the most power with a mirrorless though is using one that has an Eye-Start Sensor next to the EVF. On many models such as the Fujifilm X-T20, you can set it up so that the EVF is off until you get close to it. The default mode is to use the Eye-Start Sensor to switch between the EVF and LCD which drains the battery rather fast.

Answer 2

Usually the smaller the display, the less power it needs. Modern cameras have usually quite big screens, so they eat considerably more battery life (20% could be quite accurate). On my DSLR I leave my back screen almost always turned off, using only the optical viewfinder and the battery life is much better. When it comes to EVF, the difference probably won't be as large, but still should be present.

If yes, I will next ask a question whether there is a way to keep the screen permanently switched off on models without a rotating screen.

Depends on the model. You could consult user's manual prior purchase to be sure.