Card speed / battery life correlation?

Just out of curiosity: Assuming you are a stills shooter walking around with a capable contemporary camera, What does it cost you to have old kind of sluggish but cheap memory cards inside?

There are the obvious things like: it will take ages to flush your buffer and you can't chimp as quick as with another faster card. But will you also drain your battery way faster and get significantly less shots per charge?

Any observations or research on that topic somewhere? Thanks in advance! I'd simply love to get a more detailed understanding of how things work.

Power consumption tends to increase exponentially with data rate, so I would expect faster transfer rates to deplete a battery quicker. But then you're writing/reading for a slightly longer time with a slow card. Nett result: I'd be very surprised if there was any noticeable difference in battery life at all.

Measurable? Maybe, but of any practical consequence? Doubtful.

If you're chimping and waiting for the card, the screen is probably still on. So I'd expect the battery to suffer just because of the increased time you're sitting there looking at the camera. I'd expect slower write times also to be negative for battery under normal use (given that a chunk of camera circuitry has to be active), but it is true that writes to flash storage are relatively power-hungry, and writing to a fast card may well use more current. I've certainly had fast USB sticks warm up.

I'm vaguely reminded that Top Gear once put a litre of fuel in a Prius and a BMW M3. They then ran the Prius around the track as fast as it could go, and followed it in the M3 (which could keep up easily). The Prius ran out of fuel first. Not a massively informative test, but a useful analogy for having an over-specced card running well within its limits.

As with Joe, I'd expect the effect to be measurable, but probably lost in the noise compared with the rest of the current required by the system. That may not be so true of a device with a small sensor and its screen off, recording video over a long time (say one of the Blackmagic micro cinema cameras).

My old D70 and current D7200 are stingy on battery life. Though I used the fastest or close to fastest card that I could.

I've never yet had to switch to my 2nd battery, during a shoot. And that included shooting a 6 hour, 4 game, basketball meet where I am pretty sure that I shot over 1,000 shots. My feet gave out before the battery.

Even if a slower card did take more power, the practical effect on the battery would likely be zilch. I would still be able to do my shoots on 1 battery.

Good point @gary Nakayama as far as SLRs are our only concern. I never ran out of a Pentax proprietary battery either and my Canon made it through 1800 machine gunned shots. But with Leica M starting around 300 shots per charge or mirrorless I thought batteries became something to worry about once again.

Thanks everybody for the replies.

Ah yes mirrorless.

Extra power needed for the EVF and who knows what else.

Yes, you are right. You have to carry spare batteries. I could go through a battery in a single game, and be into the spare :(

I don't see the fuss. 3rd party batteries don't cost a lot, and take a lot less time to change than a 35mm cassette ever did.

Carrying spares and changing batteries is just part of the routine.

A bit more annoying if a tripod covers the battery door, but it's not the end of the world.

But with Leica M starting around 300 shots per charge or mirrorless I thought batteries became something to worry about once again.

Mirrorless cameras run the sensor and at least one of the viewfinder or rear display constantly - historically this has actually caused the sensor to get warm enough to affect image quality to some extent, although that seems to be less significant in the latest generation. Leica admittedly don't have to do this, but they suffer from being a small manufacturer and arguably their electronics are a bit less refined (plus you have to take the base plate off to replace the battery, I believe). With the exception of transmission via Eye-Fi and related technologies (which specifically avoid powering down the card), I don't think anything should be driving current through the storage circuitry until actual image writes happen. So while battery life has a reason to be worse on mirrorless cameras than for a DSLR that only has to drive its meter and viewfinder LEDs, I don't see an obvious reason for the storage medium to come into it.

I'm quite grateful that I very rarely need to change batteries on my D810 (I've gone through many thousands of shots at a wedding with only a couple of batteries), I agree that spare batteries aren't the end of the world. The biggest problem I've had with batteries has been with an Eos 620 film camera, which I discovered was slowly draining its batteries left on the shelf.