How to Replace Dead Batteries in a Cordless Vacuum Cleaner
Cordless vacuums are powered by the energy stored at onboard batteries and as long as the batteries are going on strong, so does the vacuum.
However, after some time, batteries lose their capacity and they are unable to provide strong enough current. When that happens, cordless vacuums can't operate as long and as strong as they used to - it is time to replace the batteries or get the new cordless vacuum.
Published: November 16, 2020.
Rechargeable Lithium Batteries - Intro
Cordless vacuums come either with a replaceable battery or with a fixed battery.
If You have a model with a replaceable battery that is showing signs of aging, simply order a new OEM battery and that's all.
However, if your model doesn't have a replaceable battery, but the battery is failing, while the rest of the unit is in perfect working order (and the warranty period is gone a long time ago), You can either take/send a unit to a repair shop and let them replace the batteries for You, or you can replace them by yourself. Or, you can recycle your old cordless unit and buy one with a replaceable battery.
Note: It is highly recommended to let professionals either replace the battery or recycle the whole unit. Whatever You do with your unit, it is your responsibility and with lithium batteries being able to store and release large amounts of energy quickly, they are not something to play with ...
When replacing old batteries, be sure to replace old batteries with new batteries that have the same or better features than old batteries - but, they must be of the same chemistry.
For example, Lithium Iron Phosphate (LiFePO4) batteries are very safe batteries, but they are not so common in high-discharge applications. Also, their nominal voltage is 3.2 volts, while other lithium chemistries have a nominal voltage of 3.6-3.7 volts. Obviously, if your cordless unit is using 3.2-volt batteries, don't replace them with 3.6-volt batteries and vice versa - these batteries can easily overheat, catch fire, and even explode. Seriously.
Other important details to consider: the size of the battery, capacity, maximum charging/discharging current, presence of the Battery Management System (BMS), and similar.
In this example, I am going to replace batteries in an older Electrolux convertible 2-in-1 stick/handheld vacuum, which is very similar to Electrolux EL3020A UltraPower Studio.
Again - should you decide to replace the batteries on your own, it is your own responsibility if something goes wrong...
Detach the handheld vacuum from the rest of the unit and locate the positions of the screws - also, check what kind of screwdriver they require.
Very often, units with non-replaceable parts, batteries in this case, come with awkward looking, non-standard screw heads - is it deliberate in order to prevent people from opening the devices or not, I don't know.
Anyway, the author of this article has a Master's Degree in electronics with a decades-long habit of disassembling and (usually) assembling things and devices.
After opening, clean the dust and try to locate all required parts while taking notes (and/or photos). As one can see, this model uses batteries without built-in BMS, but the BMS is present in the form of a controller board.
This Electrolux cordless vacuum uses three lithium batteries with a nominal voltage of 10.8 volts (3 x 3.6 volts = 10.8 volts) - so, it is NOT using 3.2V Lithium Iron Phosphate (LiFePO4) batteries.
Now, gently pull-out and take apart (but don't break any connections!) the motor, battery pack, and the battery controller.
And this is the battery, one of three - lithium 3.6 volts high-discharge 18650 battery with soldering tabs.
Now, take the blank sheet of paper and draw a wiring diagram, while at the same time add labels to all three batteries - no photos here, since this activity is highly individual.
Also, if You can't label it on your own, please, do yourself a favor and take the unit to some vacuum repair shop or get another unit.
After some googling around, I have found out that these LG batteries don't have built-in BMS, can come with or without soldering tabs, feature a nominal capacity of 'only' 1500 mAh, but they are able to provide 20+ Amps constantly (15+ C discharge current).
Since the new vacuum was able to operate for 10+ minutes, it means that the new batteries must have a capacity of at least 1500 mAh and a maximum constant discharge current of 6+ C.
Note: low-discharge 18650 batteries feature nominal capacity in the 3500-5000 mAh range, but they often can't support more than 1-2C constant discharge currents. Such batteries will die very soon in high-discharge applications, despite their initially higher capacity.
When new batteries arrive (may be ordered from online shops and with fast delivery, they may arrive within 24-72 hours), remove (desolder the tabs) the first old battery, and attach (solder) the first new battery. After that, do the same with the second and third old/new battery - this is the safest way of replacing old batteries with the new ones while avoiding mistakes.
Note: before soldering new 18650 batteries, it is a good practice to recharge and equalize them first using a smart lithium battery charger.
Now, return the batteries and other parts to their original position and assemble the unit which is ready for the first cleaning task.
Note: this unit features label Li-21 suggesting that it comes with ~21V lithium battery - no, it is not, it is just good marketing :) but it still vacuums well...
Few More Notes ...
If You are looking for a new cordless vacuum cleaner, if possible, go for the unit that features a detachable battery - such batteries may be replaced by simply ordering the new one, without the need of taking/sending the unit to a repair shop or disassembling it at home (at your own risk).
Some of the recommended units include:
Long Story Short: When looking for a new cordless vacuum cleaner, always choose according to your own needs and personal requirements.
And when replacing dead batteries, it is the best practice to take the unit to the repair shop and let them do the job or get a new one. But, if you know what are you doing, you can replace dead batteries on your own, just be sure to use the batteries with exactly the same chemistry and the same or better features.
Of course, too good new batteries (larger capacity, lower internal resistance) may overload original battery charger too much, causing it to fail, but that is whole another story ...