The most power-efficient phones: best battery life per mAh
Perhaps the best example is Huawei, with several 4000mAh flagships announced by now, but also Samsung, whose Galaxy Note 9 is landing with such a capacity for the first time. Still, what's the point of chasing the mAh count if the phone's hardware and software combo can squeeze it dry in no time? That is why we wanted to check which phones did best on our demanding battery test with the least capacity - the ultimate optimization challenge if you will - normalizing their endurance for easier comparison.
Methodology: [battery life (min.) ÷ battery capacity (mAh)] × average battery capacity = normalized battery life
We took the results from our battery life tests (in minutes) of 21 noteworthy devices from this and last year in two categories - phones with QHD (1440p) resolution and above, and phones below that high-res mark. We then divided them by the capacity of their respective batteries (in milliampere-hours). For each device, the resulting value (min/mAh) is then multiplied by the average battery capacity of all phones in the group, so that we can have the equalized battery life, i.e. how long would each phone last if all had one and the same capacity. Here's what we found in the two categories.
NOTE: This ranking doesn't show which phone has the best battery life. What it does is it shows us which are the most power-efficient smartphones out there!
Phones with QHD (1440p) or above displays
When it comes to endurance on a charge from flagships with 1440p displays or higher, we noticed a consistently worse performance compared to those with similar specs but lower resolutions. Granted, the default screen resolution on phones like the Galaxy S9 is FullHD+, but there are still more than 4 million pixels that have to be lit up. That's opposed to two million or so on "real" FHD displays, so it doesn't help to nudge the battery life up even one iota. Twice the number of pixels to push is perhaps the single biggest reason for QHD phones to score on average a 20% shorter endurance on a charge compared to the lower resolutions.
QHD or bust? Not so fast...
With that being said, there are still some outliers to rank well in this category, too, mainly phones with OLED displays (dare we say PenTile pixel matrix?), as well as the LCD-laden U11 whose result on our tests, as well as anecdotal evidence from its owners, show that HTC did a good job pairing hardware and software.
Samsung is also not that bad in battery life when you normalize for the battery capacity in its phones, with the caveat that these are the Exynos models. After all, the tests are only able to shoe the screen-on time duration in a standardized situation before the software has started to gum up the works with a few months of usage.
Phones with less than QHD (1440p) resolution
Considering that the difference in pixel density between the two groups is barely perceived with the naked eye, manufacturers that aren't blindly chasing the resolution count seem to be doing a smarter job, as we can enjoy their phones much longer on a single charge. Even though the QHD+ group above has slightly larger batteries on average, they fare about 20% worse than the "below QHD" group here.
Apple's iPhones seem to be the best performers in that cross-section, as Apple designs its own chips and software, optimizing the heck out of its phones' power draw. This way it shoots a few birds with one stone - it can put smaller batteries in its handsets than the competition, achieving economies of scale, and that also leaves a place for extra components to sprawl inside so that its handsets land thinner.
Sony and Motorola have traditionally eked out good battery life from their packs, and the stats show it. Samsung is doing well, too, but here we have to note that it's the Exynos version of its phones that perform in the top results, while the Snapdragon ones that the US gets are consistently scoring a tad worse in battery life than their Exynos counterparts.
One thing is for sure, though - if you like a phone with a high-res display, wait for its battery life tests. All other things being equal, its endurance on a charge will be much worse than phones with sub-1440p resolutions, all for a pretty negligible difference in perceived pixel density, at least with the naked eye. Are you still chanting the "QHD or bust" mantra?