When used properly, small handheld cordless vacuums can last for a really long time, often as long as their batteries are good. When batteries die, it is very easy to replace the dead ones. Although small handheld cordless vacuums are relatively cheap, their batteries are often much cheaper. Today, I will show you how to replace old rechargeable batteries in handheld cordless vacuum cleaners. Read the guide below and see the detailed step-by-step instructions!

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What to Do When the Rechargeable Batteries Run Out of “Juice”?

If you don’t like DIY projects, perhaps the best thing to do is to take your cordless vacuum to repair shop and ask them how much will cost to change the batteries – sorry to say, unless you do it yourself, in most cases, it is cheaper to buy a new cordless vacuum cleaner.

However, if you don’t mind spending some time, you can have fun, spend just a few dollars/euros and repair your vacuum in no time. Before you begin, however, don’t forget to make sure you know everything there is to know about vacuum cleaners’ batteries in general!


Whatever you do, it is your own responsibility. Any damage or injury caused by following or using the information in this article or other articles on this site is your fault, not mine or ours. Please, read our disclaimer on our main vacuum cleaner guide page!

How to Replace Old Rechargeable Batteries In Handheld Cordless Vacuum Cleaner

After many years of use and abuse, our trustworthy Bosch cordless vacuum started to show signs of old age, so it was time to buy a new one or change its batteries.

Before making such a decision, it is good practice to disassemble the unit, clean it with compressed air thoroughly, and check if it works properly. Often, dust and corroded contacts can slow down the motor, although the batteries are still good.

Also, when taking it apart, take photos, just to be sure how to assemble it properly later and note the type and size of the batteries.

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More expensive units can be disassembled, usually, using most common screwdrivers, but cheap vacuums often require sets of special tools just to open them. Is this some kind of competition in China, I really don’t know 🙂

Carefully open the unit and remove motor with batteries from the rest of the vacuum.

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It is obvious from the start that this vacuum uses three NiMH battery, connected in battery pack using soldering tabs – 3.6V battery pack is much weaker than, for example, 12 or even 18V packs, but it is cheaper.

When batteries are removed, it is good practice to clean the motor with compressed air – although these motors spin fast, be careful not to over-rev it. A drop of WD-40 on the motor’s shaft sounds like a good idea, but although WD-40 can help in decreasing the friction, it also attracts fine dust particles that can stick to it and the shaft, increasing the friction in the future.

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Layout of the batteries. If unsure, it is good practice to take notes and few photos when working with new devices.

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Industrial soldering of batteries (actually, tabs are spot welded) – unavailable at home, but with a good soldering iron and steady hands, batteries can be soldered at home in no time, especially when soldering tabs to tabs and NOT tabs to batteries. Soldering tabs directly to the batteries at home is possible. However, it can damage the battery, to say the least. Not recommended!

A Few Words on the Batteries Themselves

Individual batteries are around 43mm long and have 23mm in diameter. These are sub-C batteries with soldering tabs – very common batteries often found in various cordless tools.

  • However, their capacity is not shown. Most modern NiMH rechargeable sub C batteries designed for use in power tools that come with soldering tabs have capacities between 2800 and 3500 mAh.
  • If the capacity is higher (up to, or even higher than 6000 mAh), check maximum continuous discharge currents of such batteries
  • If it is below the maximum continuous discharge current of your cordless vacuum, a too strong cordless vacuum can discharge batteries too fast and damage them over time.

Good NiMH battery can withstand 500-1000 charge/discharge cycles, but high capacity battery designed for low current applications will not last that much. Not even close.

  • So, when choosing batteries for high-drain applications, check capacity, but also check max drain current, shown as xC, where ‘C’ is capacity in mAh or Ah and ‘x’ is the strength of drain current.
  • For example, a 3000 mAh battery that can provide 15C current safely, can provide 3×15=45A of current. That is some serious current.

I was lucky to find locally 2800 mAh NiMH sub C batteries (max current 15C) at a bargain price (although I was hoping to find 3300 mAh or similar, at least 10C, batteries). They even soldered them for me for free. Fortunately, I had all photos of the disassembled vacuum on my phone, so they could double-check everything.


Even if you can solder them at home, if you have a professional do that for you (and for free), don’t think twice …

If you want to order or check sub C NiMH batteries online, feel free to check NiMH sub C batteries on Amazon.

  • When the battery pack is done, assemble the vacuum cleaner and let it charge for at least 12-16h.
  • The charging current of my charger is 225 mAh, so to fully charge fully discharged 2800 mAh batteries, it takes at least 12-13h.

Wrapping Up the Battery Replacement Project

Although new NiMH batteries are never fully discharged, I have left my vacuum for 24h in the charging station. After that, I have fully discharged it and charged it again for 24h before considering the batteries replaced.

Six months later, they are still going strong – from time to time, I let my kids play with the cordless vacuum and to fully discharge it. NiMH batteries don’t have issues with memory effect like NiCd batteries, but who knows … 🙂

Long story short

I have replaced batteries at just a fraction of the cost of a new cordless handheld vacuum cleaner. Even so, such vacuums can be found really cheap (30-50 dollars/euros) and if you really like your vacuum and don’t mind some DIY work, replace the batteries.

Otherwise, buy yourself a nice, brand new, cordless handheld vacuum cleaner!