/ Sustainability

Lithium-ion batteries: why we’re changing our tests

A Best Buy should outlast its battery. Here’s why, thanks to your feedback, we’re changing the way we test products with lithium-ion batteries.

Battery failure is consistently one of the common faults in many cordless products. With cordless vacuum cleaners our data shows that more than a third (34%) experience a battery failure.  

We looked at cordless vacuums in a recent sustainability investigation and found a number of models where the battery is locked in and cannot be replaced.  

If a problem with the battery occurs, your vacuum could start to gather dust instead of collecting it. For people who have bought a vacuum on the basis of a Which? Best Buy rating, this is far from the ideal outcome.  

Not only that, but it’s also very damaging for the environment. It’s not acceptable that the entire product should end up in landfill due to the failure of one small, otherwise-replacable component.  

Changing our tests

Back in March 2019, our head of product research stated in Which? Magazine that we couldn’t ignore product sustainbility; our reviews had to change.

As of this month, that’s exactly what’s happening. We’re changing how we test products that run on lithium ion batteries.  

If the model does not have a replaceable battery, it simply cannot be a Best Buy. If an existing Best Buy has a battery that isn’t replaceable, it will lose its Best Buy status. 

As well as vacuum cleaners, this rule will apply to other devices powered by lithium-ion batteries: 

🔋 Chainsaws

🔋 Electric bikes

🔋 Grass trimmers and strimmers

🔋 Handheld vacs

🔋 Hedge trimmers

🔋 Lawn mowers

🔋 Pressure washers

🔋 Robot vacs

These are all products where we know the battery is one of the leading causes of early replacement.

Thank you

This is one way in which feedback from our members is turning into action. 

Keep sharing your experiences (sustainability or otherwise) here on Which? Conversation; we’re listening, and we’re grateful in how you are helping us shape the future of product testing. 


Excellent stuff.

I note – perhaps understandably – mobile phones and tablets are not in the list (probably because all of these in recent years have had sewn-in batteries). Space is a premium on such products so it is perhaps understandable.

The trend for laptops to do the same though is somewhat annoying. Should they be added to the list too or are they too far down the road of sewn-in batteries?

Most consumer laptop batteries can still be replaced but this does now require opening the laptop case instead of just detaching the battery. For example, see:- https://www.ifixit.com/Guide/MacBook+Air+13-Inch+Early+2015+Battery+Replacement/40697

Many other laptops now crib the form factor developed originally for machines such as the MacBook Air. With this design, almost all the space under the palm rest is taken up by the battery.

Some more recent laptop designs (see for example:- https://www.vice.com/en_us/article/gybwxw/the-5-year-quest-to-unglue-the-macbook-pros-battery) now have glued in batteries, which is not so great for sustainability.

The iFixit videos are very good and helped me replace the battery of an iPhone 5s. It was stuck in with hot-melt glue, which will probably need to be heated before the battery can be removed. Glued-in batteries are common in Apple products and perhaps others. I’ve not opened other makes but seen glue used to retain the battery in sat-navs. I don’t see why batteries cannot be retained in other ways, which would make replacement much easier, but what we really need is batteries that can be replaced without tools.

Another challenging problem for those who want to replace batteries in phones and tablets is that removal of the screen usually requires heating with a hot air gun or a powerful hairdryer to soften the glue around the edges so that the screen can be prised away. This may not end well for the beginner, though it is routinely done to replace broken phone screens.

Sadly, I am not aware of any popular modern smartphone with a battery that can easily be replaced.

Happy to see mention of iFixit here. As far as I know there is no UK equivalent.
I have long thought that IFixit was a natural partner for Which, sharing many of the same objectives. I would like to see Which reports include a repairability index, perhaps sourced from iFixit. Unfortunately most of the Which reports seem to be dumbed down and any non trivial technical information is omitted.

I would certainly like a Which best buy requirement to be an affordable, available replacement battery where applicable most certainly including mobile phones.

Thanks for this Convo, Matt. Sometimes replacement batteries can be very expensive. For example I’ve seen new batteries for a cordless drill costing almost as much as a new drill at sale price. I wonder if Which? reviews could give the price for a replacement battery to help the reader make an informed choice.

I very much agree with Roger about laptops with batteries that cannot easily be replaced.

I’m not sure how many people have cordless chainsaws but cordless vacuum cleaners have proved very popular, and it is encouraging that I could see only a couple of models that were denied the Best Buy accolade because they did not have replaceable batteries. I’m not tempted because I have a couple of old corded cleaners.

Any “expensive” product with a battery should, in my view, allow user-replacement; that includes tablets, mobile phones. We should not sacrifice sustainability for style. I also think we should work towards generic batteries, even if they are mounted in a dedicated housing as, for example, in power tools. We could then see third party providers of the cells rather than having to buy proprietary, and probably unnecessarily expensive, OEM replacements.

A big problem with non-manufacturer batteries is all the fakes out there that can be dangerous.

That certainly puts me off buying cheap replacement laptop batteries. Hence, some of my older laptops are just used as “mains only” devices.

I’ve replaced phone batteries and faced the same problem of deciding whether they were “proper” batteries, even though sold as Nokia. Just like any other on-line purchase it is always tempting to buy on price but I try to find reputable vendors, or the manufacturer’s outlet.

Maybe Which? could do some of this hard work for us and advise of reputable sources online.

Early battery-operated products generally used NiCd or NiMH cells and a temperature sensor. Once fully charged the cells get warm and when this is detected the charger either shuts down or greatly reduces the charging current.

Lithium rechargeable batteries offer many advantages over the older types, which is why they have become so common in household products. Although 18650 cells have become by far the most commonly used size of lithium rechargeable (much in the same way that AA cells are by far the most common type of non-rechargeable cells), there is a complication that will make it more difficult to have battery packs that are exchangeable between products from different manufacturers. Lithium batteries must be protected not only from overcharging but from discharging too far. If they are over-discharged they become useless. The result is that battery packs have been complicated and contain a circuit board with complicated electronics. (For anyone interested there are YouTube videos showing what can be found in battery packs.) In order to achieve interchangeability of battery packs, there are two options: either the manufacturers agree on a common standard or alternatively the standard is produced and the manufacturers comply with it.

I found this video quite interesting:- https://www.youtube.com/watch?v=h0G8y-Nur7w&t=555s

Thanks Derek. I had been looking for a YouTube video showing the electronics that is used in lithium battery packs, and this is very good example. I don’t understand why such complex electronics are needed. Lithium battery packs will perform best if there is cell equalisation to compensate for the fact that some cells in a pack are always weaker than others. Without equalisation, the run time of the product will decrease faster.

The electronics can be in the charging unit rather than in the battery pack, as the Bosch one demonstrates – seemingly. I’d like to see battery replacement made as easy as possible and sources of reputable batteries listed.

Unfortunately, it’s not that simple. As I explained elsewhere, lithium batteries must be protected to ensure that none of the cells over-discharges, otherwise the battery will be wrecked. That means that there must be electronics in the battery pack or in the product that it powers. Additional electronics is needed to control the charging because lithium cells can also be damaged by overcharging. This electronics can be either in the battery pack or the product itself. An advantage of having all the electronics in the battery pack is that if there is a failure the product does not have to be replaced or repaired, which would probably not be economically viable.

I have a small and a large Bosch cordless drills, both for convenience and so that I can do work where there is no source of mains power. I don’t know whether or not the battery packs contain electronics, but some Bosch battery packs certainly do: https://www.protoolreviews.com/tools/power/cordless/batteries-chargers/bosch-batt622-6-ah-battery/16453/

Looking to see if it would be possible to buy a spare battery for my small Bosch cordless hedge trimmer I found one on the RS site. The price is more than I paid for the hedge trimmer. 🙁

Out of interest I opened the battery pack for a Bosch cordless drill and found that it contained five Samsung 18650 lithium cells, a temperature sensor stuck to the side of one cell, a diode a resistor and a non-replaceable fuse. Anyone who could wield a soldering iron could replace the cells and the cost of replacement would be about £30, buying from a reputable but expensive source. Even if a battery pack contains a mass of electronic components it may still be easy to replace the lithium cells.

The Bosch battery pack did not contain complicated electronics, as the video demonstrated, and there seemed no problem with reliability. Is there evidence to the contrary?Nevertheless the key is to make battery replacement in whatever appliance simple. Hopefully any electronics necessary will match the life of the appliance.

I’ve given you a link that shows a Bosch battery that does contain complicated electronics, Malcolm. That is important for frequently used products such as cordless drills used by tradesmen otherwise the effective working capacity of the battery will progressively deteriorate. Here is some information on Wikipedia: https://en.wikipedia.org/wiki/Battery_balancing Anyone who buys a cordless vac will not want one that gradually loses run time. Cheap power tools like my Bosch cordless drills don’t have this refinement but I don’t use them much.

I was simply going by the video Derek posted.
I’ve no problem with battery packs containing more complicated electronics to control charging and optimise appliance performance but clearly they add to the possibility of shorter life and increase the cost. If the cell life is such that they need replacing – either through failure or just reduced charge – then I am suggesting they should be easily replaceable, and the electronics should be robust.

The question is, how do we weed out the good from the bad when testing? Generally with electronics it is excessive component temperature that determines life (assuming good quality components are used); the industry I was in used electronics in arduous situations with long life – necessary for commercial products but it was not at untoward cost. I wonder if Which? do any such tests?

Cell balancing circuitry is necessary to maximise battery life, as I have explained. It has to be in the battery pack or in the product itself. If circuitry is well designed it should outlast the product. The introduction of microcontrollers has led to a considerable reduction in component count, which is a cost saving for consumer products.

Lithium batteries can have very respectable lives if little used and lose little charge in storage. For example my Dremel has a 2006 battery. The problem arises when these batteries are used heavily, which is why mobile phone batteries can fail after two years.

I don’t know how long batteries for cordless vacuum cleaners last. Obviously use will be a factor but so will circuit design. Because of the high currents involved and the need for reliable connections, it’s not really practical to have cells that can be changed in the same way that we do with a torch or a remote control. I would like to see cells that are easily replaceable without the need for tools, say using push-on tags rather than having to solder the connections.

It would be interesting to know how long cordless products such as vacuum cleaners last. I cannot remember if this has been covered in Connect surveys.

My concern is to support Which? in making batteries replaceable and, although they don’t state it, at sensible cost. I’d hope this will develop into replacing cells in existing housings, rather than replacing a whole assembly, to help reduce the waste of resources. I’d also like to see incentives to recycle the used cells to help the environment.

I think it’s great that Which? have are looking at sustainability. We and others have discussed batteries many times in numerous Convos.

I gave the example of a lightweight hedge-trimmer where a replacement battery cost would more than what I payed. Fortunately I have found cheaper sources of the battery in question but price is often a problem. It would be great if Which? could give us the approximate cost of a spare battery in reviews, which could make a more informed choice about which make and model to buy.

As an incentive for recycling used batteries I’ve suggested a charge on new batteries and a refund for trading in old ones. Maybe there is a better solution.

It is very easy to have user-replaceable batteries for products such as cameras with low power requirements, but once again it would help if Which? provided advice on cost and availability of spares in its reviews.

How environmentally friendly are some of these battery operated products?

Take a vacuum cleaner . . .

A mains powered vacuum cleaner uses the amount of electricity it needs to do the job then the cleaner is put away for next time. My previous vacuum cleaners lasted at least 15 years and my current one must now be about 10 years old.

A battery operated vacuum cleaner will still need electricity to charge the batteries maybe not every use in early ownership, but I will bet it won’t be long before they don’t hold their initial charge. We had one in a US holiday rental that lived permanently on its charging base and was always on, so would presumably keep charging as required between use. I can’t see a vacuum cleaner battery lasting more than a couple of years.

To me, batteries in vacuum cleaners seem an unnecessary waste of earth’s precious resources. Batteries have their uses, but not when they are used in an appliance that works better on electricity.

Not only do batteries have a relatively short life that will be much shorter than the life of the product, they use what are known as rare earth minerals. These minerals are not necessarily rare, but they do a lot of damage to the planet in acquisition, processing, life and recyclability.

I agree with that, alfa. There is the minor (very) inconvenience of having a trailing mains lead but you don’t have to carry the weight of the battery around with you, and it only dstops working when you want to. There are conversion losses in charging the battery, as well as the resources needed to manufacture it. Derek’s video of power tool battery packs was quite illuminating, most of which seem to have complex electronics that can shorten life. A small battery cleaner is convenient for the car, but I’d stick with a mains one for the house.

Mobile phones are rightly criticised as being environmentally unfriendly because of the batteries and electronics they contain, but the same applies to cordless vacuum cleaners, power tools, etc. I’m happy with using corded vacuum cleaners and the one I use most of the time is about 20 years old. I use an older one to clean the car or for a quick clean I have one that plugs into the cigarette lighter socket. I chose the plug-in car vac in preference to the rechargeable version because it was cheaper, more powerful and there are no batteries to fail.

I don’t know many people who have cordless vacs (but it’s not something I discuss very often), but they are popular. Perhaps Which? could give us some information about how long the batteries are likely to last in reviews and that might encourage consumers to decide whether or not it’s worth going cordless.

Alfa questions the wisdom of leaving products on continuous charge and so do I. Whatever the manufacturer may claim, I cannot see any benefit in doing this. With older NICd and NiMH batteries it gradually damages the batteries and these are still widely used in small electrical goods including electric toothbrushes. Modern products use lithium batteries that are protected from overcharging and their chargers often consume little power. It’s easy to check with a plug-in power monitor.

Alfa, the 16 rare earths are indeed rare: Lanthanum,Cerium,Praeseodynium,Neodymium,Promethium,Samarium,Europium,Gadolinium,Terbium,Dysprosium,Holmium, Erbium, Thulium, Ytterbium and Lutetium. Holmium is used in a medical laser used to remove enlarged prostates. Gadolinium is used in medical MRI scanning work.
I think that an alloy of Neodymium and tin is used to make the screen of mobile phones.
Most of them are mined in China. I hope that they are all being recycled.

I wonder if the answer would be set up a scheme that would pay a few pounds for scrapped products containing rare materials to discourage them landing up in landfill. This could be funded by a charge on new products. This already happens with car tyres.

Welcome back Dave. We don’t see you here very often.

A couple of years ago I spotted a Vileda Windomatic battery operated glass cleaner going cheap, so I thought I’d get it for our new shower cubicle. I charged it up to make sure it worked and then like so many gadgets it got put in a cupboard and forgotten about. Fast forward two years and I tried to resurrect it – no dice, battery refuses to charge. Looked on t’internet to find it’s a well-known problem – if the battery discharges below a certain point then it will not recharge. There are videos on how to jump-start it as it were by taking it apart and attaching a battery across the rechargeable battery terminals along with warnings about them not being responsible if it explodes in your face! Don’t think I’m going to risk it.
So this is now essentially a piece of (unused) junk ready for the skip. Very poor design in my opinion. Which? might like to take this up with Vileda as other buyers may get caught out too.

It looks as if your Vileda uses a single 18650 3V lithium rechargeable cell, Colin. As you have discovered, lithium cells will not recharge if over-discharged. I expect that the cell will be wrecked but maybe try connecting a small 9V battery – the type used in smoke alarms across the lithium cell for a short time with the charger disconnected. There is not enough energy to cause an explosion. 🙂

Replacement 18650 cells (often marked 3.6 or 3.7 volts rather than 3 volts) are widely available but if the original is soldered in place you would need one a tagged cell. It’s worth bearing in mind that lithium cells are always sold at least partly charged and must not be short circuited or installed the wrong way round.

Until recently, Miele was the only major manufacturer of vacuum cleaners not to offer cordless vacuum cleaners, but that has changed and Which? had done a First Look review of one of them: https://www.which.co.uk/reviews/cordless-vacuum-cleaners/miel-triflex-hx1-pro

A shame you aren’t extending this in some way to mobile phones. Although I appreciate that excluding those with non-removeable batteries would leave your best buy list looking a little thin to say the least!bThere are still a few mobile phones that have removeable batteries but none of the high end, high scoring ones as far as I’m aware. I’ve seen various justifications for non-removeable batteries but I can put up with a few extra grammes and a couple of millimetres in tickness and, in reality, it’s surely just one of the plethora of shady tactics used by phone manfacturers to encourage us to replace what can be a very pricey piece of kit every year or two. Something should be done about it.

As to vacuum cleaners, I have a perfectly good mains powered machine and, like most people, an accessible power outlet in every room so I struggle to see the attraction of battery powered vacuum cleaners.

Tim says:
7 August 2020

Good, about time………

Tim says:
7 August 2020

Most mobile phones now you can’t change the batteries, this defo needs to change and added to your list !!