How We Measure Battery Life, and Why Manufacturer Figures Differ (Pixel 9 Pro)
How We Measure Battery Life, and Why Manufacturer Figures Differ explained, with the Pixel 9 Pro's own measured figures as the worked example: quoted battery figures are produced under conditions almo...
Priya Raghunathan
The short version
Pixel 9 Pro, weight 199g — How We Measure Battery Life, and Why Manufacturer Figures Differ. Measured on hardware rather than argued from theory, on a device we rate for the most consistent computational photography of any phone.
Quoted battery figures are produced under conditions almost nobody replicates. Ours use a fixed brightness and a scripted workload so numbers stay comparable.
Why this matters: Battery is consistently the specification buyers care about most and the one most loosely reported.
What is going on underneath
We set the display to a measured 200 nits rather than a percentage, disable adaptive features that vary between devices, and run the same mix of browsing, video and standby. The result is not the best number a device can produce — it is the number you can expect.
In daily use
Take the Pixel 9 Pro as a worked example. The camera bar finally sits flat on a desk. That is the difference this makes once you stop reading specifications and start using the thing.
| Specification | Pixel 9 Pro |
|---|---|
| Display | 6.3in LTPO OLED, 120Hz |
| Chip | Tensor G4 |
| RAM | 16GB |
| Battery | 4700mAh |
| Charging | 27W wired |
| Weight | 199g |
| Screen-on time | 6h 40m |
The spread across devices
One worked example is an anecdote. Here is how the figure that drives this behaviour actually varies across the hardware we have measured in this category — same test, same conditions, so the spread is real rather than an artefact of who reviewed what.
| Model | Display | Price | Our score |
|---|---|---|---|
| Pixel 9 Pro | 6.3in LTPO OLED, 120Hz | £999 | 4 / 5 |
| iPhone 16 Pro | 6.3in LTPO OLED, 120Hz | £1099 | 4 / 5 |
| Galaxy S25 Ultra | 6.9in LTPO AMOLED, 120Hz | £1249 | 4 / 5 |
| Nothing Phone 3 | 6.7in AMOLED, 120Hz | £579 | 4 / 5 |
What good actually looks like
It helps to have a number in mind before you start comparing. Across the smartphones we have measured, the useful thresholds are the ones where a difference stops being visible: below them you notice, above them you are paying for a specification rather than an experience. The Pixel 9 Pro reports 6.3in LTPO OLED, 120Hz for display, which sits comfortably on the right side of that line, and Tensor G4 for chip. Treat anything materially below those as a real compromise and anything materially above as a number you are unlikely to feel.
What people get wrong
- A larger battery always means longer life, when efficiency varies enormously
- Fast charging damages a battery meaningfully in normal use
- Closing background apps extends runtime
How to check this on your own device
- Reproduce the conditions rather than trusting a one-off reading — run the same task three times and take the average.
- Note the figure your device reports and the figure it actually achieves; on the Pixel 9 Pro those diverge under sustained load.
- Change one variable at a time. Brightness, background sync and ambient temperature all move this number independently.
- Compare against the manufacturer’s stated figure and treat any gap as the cost of real-world conditions, not as a fault.
- Repeat after a firmware update — this is one of the numbers that moves without an announcement.
Where it shows up on a spec sheet
On a smartphone listing this usually appears as the display line — the Pixel 9 Pro quotes 6.3in LTPO OLED, 120Hz. That figure is necessary but not sufficient: the chip entry (Tensor G4) constrains it in practice, and the two are almost never presented together. When you see one quoted without the other, assume the omitted one is the weaker of the pair.
How to use this when buying
Compare figures from one source measured the same way, and ignore cross-site comparisons of quoted numbers.
A battery figure is only meaningful alongside the method that produced it.
Behind this piece
Every product covered here was bought at retail and lived with for at least a fortnight before a word was written. Battery figures come from a scripted day rather than a manufacturer estimate, and sustained performance is measured warm — after half an hour of load — because that is the state a device spends most of its life in.
Where a firmware update changes a result, the piece is re-tested and the change noted rather than quietly corrected. No review unit arrives with conditions attached, and no score is agreed in advance with anybody.
Where to go next
If you are weighing this against the rest of the smartphones we have covered, the category archive lists every review in date order. The closest comparisons we have published are How We Measure Battery Life, and Why Manufacturer Figures Differ (Pixel 9a) and How We Measure Battery Life, and Why Manufacturer Figures Differ (Xiaomi 15 Ultra).
For the reference material behind these figures, the specification pages carry the measured numbers, and the common questions collect what people ask once something is in daily use.
