Watch the video to find out what it takes for a cordless vacuum to earn our coveted Which? Best Buy recommendation, and how a Best Buy could make a real difference to your home.
We've independently tested a range of big brand cordless vacuum cleaners so that you can be sure that the one you're buying really does live up to its claims.
Our reviews answer the most crucial questions about cordless vacuums:
We use fine Arizona sand to see how much dust each vacuum cleaner picks up, as well as how much it doesn't hold onto, and would therefore be leaked back into your home.
Our assessments reveal which models lose suction as the battery power decreases, so we also run the vacuum cleaners when the battery is only 20% charged.
How well a vacuum picks up hair and pet fur too, so using real cat and dog hair combed into Wilton carpet, we see how long it takes each vac to pick it up. We found one that took over three minutes, while the best took just 42 seconds.
There are huge differences in run time between the best and worst models. To measure battery life, we time how long each cordless vacuum takes to charge and how long it can run for.
Many manufacturers base their running time claims on using the cordless vacuum on the standard setting. We make sure that we test each model's running time on its most powerful setting.
To further test the battery we also test how well the vacuum cleans when only 20% of it's charge remains. The best machines will maintain excellent pick up under these conditions, but some vacuum cleaners pick up much less when the battery begins to run down.
Lithium-ion batteries always deplete and eventually die over time, and at Which?, we believe that cordless products should last longer than the batteries they come with. That's why we no longer give cordless vacuum cleaners Best Buys if spare batteries cannot be bought from the manufacturer – no matter how good the cordless vac might be.
We test the suction of each cordless model on three different surfaces - laminate, floorboards and carpet - so you know whether it will work well in your home.
Using 25g of dust for each vac, we carry out two runs on each surface type, seeing how much of the dust is in the canister at the end.
We also look at the tools it comes with, such as nozzles, to see if they're effective in picking up dust.
Because a vacuum cleaner is no good if it's a pain to use, empty and manoeuvre, we put each model through a range of ease of use tests assessed by an independent panel. We get them to rate how smooth and easy it is to vacuum on Wilton carpet, hard floors, stairs, upholstery and uneven surfaces, making a note of how heavy it feels, whether it's uncomfortable to hold and how easy it is to push and turn.
We also ask them to assess how easy it is to take each vacuum out to clean a car and also how easy it is to vacuum in difficult to reach places above shoulder height.
If that wasn't enough, we also get them to assess how easy each is to assemble and dismantle for storing, what the grip of the handle feels like, how easy it is to empty the canister, change any attachments, and read the instructions, as well as what it's like using all the switches.
Finally, we measure in decibels how loud each vacuum is - the worst get up to 88 decibels, which is the same as the noise from a busy road.
All of the assessments listed above go into making the final overall score for each cordless vacuum cleaner we review. Because we know what's most important to you, some elements are more important than others, so carry different weights:
A model has to achieve 70% of more to earn our Best Buy recommendation, and anything scoring below 45% is highlighted as a Don't Buy that we think you should avoid.