Why is the VOX number two or three times the screen-on number?

Because the backlight and video decoder are off until the camera hears a sound. A quiet night barely wakes the screen, so the cell lasts. A night of frequent wakes looks much closer to the screen-on figure.

Which? says 7 hours for video — why do shops still print 20 or 30 hours?

Those shop numbers are usually VOX, ECO or audio-only. Which?’s 7-hour video average is a lab mean across tested video parent units, not a cap on every claim. Compare the shop’s screen-on line with that average, not the VOX line.

The box only prints one number. What should I assume?

Assume it is the best-case mode until the manual names it. Look for VOX, ECO or “video streaming” in the battery chapter. If the manual never splits the figure, you have no like-for-like number.

Do audio monitors always last longer than video?

Which?’s averages say so (about 13.5 hours versus about 7), but Which? also found audio sets that died in under six hours and video sets that passed 12. The type is a hint, not a rule for every set.

Guides · Baby monitors · Spec sheets

What claimed baby monitor battery hours actually mean

Updated 10 September 2026 · Checked 10 September 2026 · By MayTally research desk — Checked against official UK sources

What do Which? tests say parents should expect?

Which? compared a 2019 survey of 1,360 parents with its own lab runtimes. Parents said they wanted about 13 hours before a recharge. Tested parent units averaged under 10 hours. The spread was wide: the shortest set died in under three hours; the longest ran nearly 27 hours. Video sets averaged about 7 hours. Audio-only sets averaged about 13.5 hours. Those figures are Which?’s tested averages, not a promise for the model in your basket.

Swipe sideways for the full table

Which? battery-life picture (parent unit)
Figure	What Which? reported	How to use it on a spec sheet
Parent expectation (survey)	13 hours on average	The overnight number many boxes imply without saying so
All tested parent units	Average under 10 hours	Treat any claim far above this as a mode, not a default
Video monitors (average)	About 7 hours	Closest match to “screen on all evening”
Audio monitors (average)	About 13.5 hours	No backlight; still not every audio set hits this
Spread in the test set	Under 3 hours to nearly 27 hours	Read the individual test, not the category slogan

Figures from Which?, “The baby monitors failing to live up to parents’ expectations”, based on a 2019 survey of 1,360 parents and Which? lab tests. Checked 10 September 2026. Which? has not published a replacement average in the public news piece; later Best Buy pages still test battery life but hide per-model hours behind the paywall.

Which?’s buying guide (updated 30 July 2026) still measures how long the pack lasts in real use. Its public rule of thumb is that a decent parent unit should last from the baby’s bedtime until you go to bed — not from 7pm to 7am with the screen lit.

How do I read VOX, ECO and screen-on on the box?

Makers print the longest number they can defend. The small print names the mode. Decode the label before you compare two boxes.

Swipe sideways for the full table

Spec-sheet decoder
Wording on the box or manual	What is usually switched off	What you are actually buying
VOX / voice-activated / sound-activated	The parent-unit screen (and often the speaker) until the camera hears a noise	Long standby, short bursts of video. Night-time hours look huge if the room is quiet
ECO / sleep / energy-saving	Radio or screen between triggers; some cameras drop to a low-power link	Same idea as VOX, sometimes with a dimmer display. Not continuous video
Screen on / video streaming / continuous video	Nothing — backlight and decoder stay awake	The short number. Closest to “I want to glance at the screen at 2am without waiting”
Audio-only mode	The display; microphone and speaker stay live	A middle number. Useful if you can live without the picture
Up to X hours	Unstated — often VOX at lowest brightness	Ignore “up to” until the mode is named

Mode names are taken from common UK manuals and retail listings (VOX, ECO, video streaming, audio-only). Hours in this table are not invented runtimes — use the Which? averages above or the mode the maker printed next to the claim.

How do I check a claim in two minutes?

Find the hours line Look on the box back, the spec table, or the manual’s battery chapter. If there is only one number and no mode, treat it as incomplete.
Circle the mode words VOX, ECO, sleep, screen on, video streaming, audio-only. If two numbers appear, the larger one is almost always the screen-off mode.
Compare like with like Put the screen-on number next to Which?’s video average of about 7 hours. Put a VOX number next to the “up to” marketing, not next to a screen-on rival.
Check which unit the hours refer to Claims are almost always for the parent unit. A mains-only camera has no overnight hours. A rechargeable travel camera has a second, shorter number — night vision cuts it further.

Philips Avent manuals show the same split in maker language: one model quotes about 7 hours in voice-activation and about 5.5 hours with the video display on continuously. That pair is a worked example of the decoder, not a runtime to copy onto another brand.

What the claimed hours are not measuring

First-week capacity. Several Philips manuals say the pack only reaches full capacity after four charge-and-discharge cycles. A new unit can undershoot the box on nights one to four.
Brightness, lullabies and night light. Manuals warn that a lit display, playback and a night light shorten the run. Those features are usually off in the VOX photograph.
The baby unit. Which? notes many cameras are mains-powered. A 20-hour parent-unit claim says nothing about a camera that dies when the socket fails.
Range or picture quality. Hours and signal are separate Which? scores. A long VOX number can sit on a set that drops in the garden.

In shortRead the mode next to the hours. VOX/ECO is screen-off standby. Screen-on is the short number and the one closest to Which?’s 7-hour video average. “Up to” without a mode is not a comparison you can use.

Does a longer battery change safer-sleep advice?

No. The Lullaby Trust states there is no research showing monitors prevent SIDS, and that a monitor cannot replace an adult in the room for the first six months. Battery-life small print is a shopping decoder. It is not a reason to move the travel cot into a different room.

Questions parents ask

Why is the VOX number two or three times the screen-on number?: Because the backlight and video decoder are off until the camera hears a sound. A quiet night barely wakes the screen, so the cell lasts. A night of frequent wakes looks much closer to the screen-on figure.
Which? says 7 hours for video — why do shops still print 20 or 30 hours?: Those shop numbers are usually VOX, ECO or audio-only. Which?’s 7-hour video average is a lab mean across tested video parent units, not a cap on every claim. Compare the shop’s screen-on line with that average, not the VOX line.
The box only prints one number. What should I assume?: Assume it is the best-case mode until the manual names it. Look for VOX, ECO or “video streaming” in the battery chapter. If the manual never splits the figure, you have no like-for-like number.
Do audio monitors always last longer than video?: Which?’s averages say so (about 13.5 hours versus about 7), but Which? also found audio sets that died in under six hours and video sets that passed 12. The type is a hint, not a rule for every set.

Sources

Official pages first. If this page and the official page disagree, the official page wins.

Which? — The baby monitors failing to live up to parents’ expectations — checked 10 September 2026
Which? — How to buy the best baby monitor (updated 30 July 2026) — checked 10 September 2026
Philips Avent parent-unit manual notes (voice-activation vs display-on hours; four cycles) — checked 10 September 2026
The Lullaby Trust — Baby monitors — checked 10 September 2026

This is information, not a guarantee of any payment, and not medical, legal or product-safety advice for your home. Prices and rules change; figures carry the date they were checked. Recall status comes from official records only — a product we cannot find is not a safety all-clear. Tell us if we got a fact wrong.