The small improvement in iPhone battery capacity

About a month ago, David Sparks wrote this wonderfully titled post on how battery life has become a prominent selling point for our laptops and tablets and phones. At about the same time, in an episode of The Prompt that I can’t be arsed to look up, Myke Hurley expressed disappointment in the pace of improvement in battery capacity for iPhones. I felt certain Myke was wrong—phones have gotten so much more powerful the batteries must have improved—so I went searching for the battery capacities of all the iPhone models.1 I made some notes and thought about writing a post about it, but never got around to it.

I was reminded of the topic when John Gruber and Guy English mentioned it on this week’s episode of The Talk Show, so I pulled out my notes from last month. Here’s list of battery specs for every iPhone:2

Model Voltage Capacity Capacity
Original 3.7 V 1400 mAh 5180 mWh
3G 3.7 V 1150 mAh 4255 mWh
3GS 3.7 V 1220 mAh 4514 mWh
4 3.7 V 1420 mAh 5254 mWh
4S 3.7 V 1430 mAh 5291 mWh
5 3.8 V 1440 mAh 5472 mWh
5s 3.8 V 1570 mAh 5966 mWh

Battery capacity is usually given in milliamp-hours. This isn’t really a measure of energy but is a reasonable proxy if the voltage never changes, which it didn’t until the iPhone 5. In the last column of the table, I’ve multiplied by the voltage to give the capacity in energy units of milliwatt-hours (and yes, I know I haven’t been careful about significant digits—sue me).

The most surprising thing to me was that battery capacity actually went down after the original iPhone and didn’t become substantially greater than that initial capacity until the 5s. The huge increase in processing capability over the past 6 years has come with only a 15% increase in battery capacity.3

It’s no secret that Apple has taken pains to make iPhones more and more stingy with power. What I didn’t appreciate until I put this table together was that the ability to still get a day of use out of an iPhone is due almost entirely to improvements in all the non-battery hardware and the software that drives it.

  1. Spoiler alert: Myke was right. 

  2. It wasn’t hard to find this info; it’s on each phone’s Wikipedia article. To exercise some atrophied scholarly muscles, I confirmed almost every spec in the table through independent means—typically by looking at a photo of the battery in an iFixit teardown. 

  3. I suppose it’s possible that the energy density of batteries has improved significantly, but I doubt it. While there’s no data on the volume of the batteries, they don’t appear to be appreciably smaller.