system
Given the following post, respond as if you're commenting on Reddit:
human
Will turning down my iPod's volume save battery life?

While turning off the screen, and various transceivers obviously saves battery life, I'd never really thought about turning down the volume until a friend of mine did this to "save power."

I'd love to know what effect, if any, turning down the volume has on battery savings.
gpt
Of course it does use more power at higher volume levels than at lower levels. The question is if the difference is significant or negligible.

For an iPod you're talking of 30mW max of power output for the headphones. To put this into perspective, if your iPod has a 2000mAH battery (at 3.7v this is 7400mWH or 7.4WH), and it lasts 40hours of playback as Apple claims, it means it uses 7.4WH/40H = 185mW in total (including the earbuds). 

A volume level of close to zero would use almost zero power, so the change from 0mW to 30mW represents a significant although not massive difference in power consumption compared to the 185mW total (at a volume level we don't know, since we don't know Apple methodologies). This leads to the conclusion that listening music at max volume compared to min volume probably leads to a difference in the order of 15% of music playback time. 

However, you probably won't be listening at max volume, and since the human hearing is logarithmic it means that to get "double the volume" you need around 10 times the power. This goes the other way too, and means that for the lower volume you probably use, it uses a lot less power. You are now most likely talking in the order of 5mW which would be close to negligible. Also, how much are you willing to lower the volume in order to save power? Realistically you will turn it down one or two levels, not from max to min as is calculated above. This will not lead to great differences.

TL;DR: Unless you compare max volume to min volume, the difference is negligible. Don't bother turning down the volume, it's not worth the minuscule battery savings.