How We Measure Battery Life, and Why Manufacturer Figures Differ (Roborock S9 MaxV)
How We Measure Battery Life, and Why Manufacturer Figures Differ explained, with the Roborock S9 MaxV's own measured figures as the worked example: quoted battery figures are produced under conditions...
Tom Halvorsen
In brief
Roborock S9 MaxV, battery 6400mAh — How We Measure Battery Life, and Why Manufacturer Figures Differ. Measured on hardware rather than argued from theory, on a device we rate for an extending side brush that genuinely cleans edges and corners.
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.
How it actually works
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.
What you actually notice
Take the Roborock S9 MaxV as a worked example. It cleared a cable, two shoes and a charging brick across ten runs. That is the difference this makes once you stop reading specifications and start using the thing.
| Specification | Roborock S9 MaxV |
|---|---|
| Suction | 10,000Pa |
| Navigation | LiDAR plus dual-camera |
| Mopping | Dual spinning pads, auto-lift |
| Dock | Self-empty, wash and dry |
| Battery | 6400mAh |
The same concept across four 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 | Suction | Price | Our score |
|---|---|---|---|
| Roborock S9 MaxV | 10,000Pa | £1199 | 4 / 5 |
| Nest Doorbell (wired, 2nd gen) | — | £179 | 4 / 5 |
| Eufy S3 Pro Cam | — | £219 | 4 / 5 |
| Meross Smart Plug Mini | — | £12 | 4 / 5 |
What counts as good here
It helps to have a number in mind before you start comparing. Across the smart Home Devices 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 Roborock S9 MaxV reports 10,000Pa for suction, which sits comfortably on the right side of that line, and LiDAR plus dual-camera for navigation. Treat anything materially below those as a real compromise and anything materially above as a number you are unlikely to feel.
Myths worth dropping
- 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 verify this at home
- 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 Roborock S9 MaxV 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 smart Home Device listing this usually appears as the suction line — the Roborock S9 MaxV quotes 10,000Pa. That figure is necessary but not sufficient: the navigation entry (LiDAR plus dual-camera) 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.
Putting it to work
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 smart home we have covered, the category archive lists every review in date order. The closest comparisons we have published are IP Ratings Explained: What IP54, IP67 and IP68 Really Cover (Aqara Hub M3) and IP Ratings Explained: What IP54, IP67 and IP68 Really Cover (Aqara Presence Sensor FP2).
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.
