The Spec Sheet Lies: What Battery Life Numbers Actually Mean
Every battery figure you have ever read was measured under conditions chosen to make it as large as possible. Here is how to translate them.
No manufacturer lies about battery life. They don't need to. They simply choose the test conditions, and the conditions are where all the work happens.
Once you know which conditions each category uses, the numbers become useful again — not as predictions, but as a way of comparing two products measured the same misleading way.
Vacuums: the number is the lowest setting
When a cordless vacuum claims 70 minutes, that is the eco mode, with the non-powered tool attached, on a full charge, at room temperature. Attach the motorised floorhead and you lose roughly half. Select the boost mode and you are into single-digit or low-teens minutes.
The useful translation: assume the headline figure applies to a mode you will rarely use, and look instead for the boost-mode figure, which is usually printed somewhere less prominent. The Dyson V16 quotes 70 minutes and delivers about 15 in boost. Both numbers are true.
Cameras: CIPA is a strange ritual
Camera battery ratings follow a CIPA standard which involves a specific, oddly artificial routine — shoot, wait, zoom, fire the flash every other frame. It is standardised, which makes it comparable, and it bears almost no relationship to how anyone shoots.
In practice most photographers get substantially more than the CIPA figure for stills, because they aren't firing a flash every second frame. Videographers get dramatically less, because CIPA doesn't measure video at all. A 620-shot rating tells you nothing about how long you can record.
Headphones: with what turned on?
A headphone quoting 30 hours means 30 hours with active noise cancelling on, at a moderate volume, over the most efficient codec. Turn on spatial audio and it drops — Bose quotes 30 and 23 for exactly this reason, and publishes both, which is more honest than most.
Higher-bitrate codecs cost battery. Loud listening costs battery. Cold costs battery. If you commute in winter at high volume over aptX, take a third off the box figure and you will not be disappointed.
E-bikes: the range figure is an Eco figure
Range is the most abused number in consumer hardware, because it depends on rider weight, terrain, temperature, tyre pressure and assist level — and the manufacturer picks all five. A 110-mile claim means a light rider, flat ground, lowest assist, ideal temperature.
The honest way to read it is as a ratio: expect roughly a third of the headline in the highest assist setting. We measured 118 miles in Eco and 41 in the top mode on the same bike. Both are that bike's real range.
The rule that generalises
Every battery figure is a best case measured under a named condition. The condition is almost always disclosed somewhere — a footnote, a spec page, an asterisk. Find it, and the number stops being marketing and starts being data.
Where a manufacturer publishes two figures rather than one, that is worth something. It usually means somebody in there argued for it.
