Cordless Tool Battery Pack Repair or Rebuild

bird dogger

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With some recent discussion about battery packs for our cordless tools and how expensive they are to replace, I thought I’d share what I had come up with to rebuild the battery packs for my cordless tools: A mini spot welder for lithium battery packs and other cordless tool packs. And if you are just a little bit tech savvy, willing to learn, careful with your planning, layout and building process, it’s not a complicated procedure. And the best part: it’s not expensive!

It started when my locksmith buddy said he had been unsuccessful finding a replacement battery pack for his portable key programmer that could operate from an internal Lithium-ion battery pack when no AC plug in was available (which happened quite often). The replacement packs were terribly expensive when they were available but everywhere he checked now the response was NLA (No longer available).

When he mentioned it to me, I suggested we just build his own battery pack and maybe a spare at the same time. He never thought that was possible. Since the lithium-ion battery is very heat sensitive, connections should not be soldered together unless you’re extremely quick! Instead, to make the connections a mini spot welder is used.

A commercial duty spot welder runs a few hundred dollars. But a portable mini spot welder that requires you to provide your own power supply (think 12vdc car battery) can be had in the $25 range. That’s what I paid for mine, including delivery.

You do have to be careful when using it, as there is no “reverse polarity” protection and you can fry the control board if you’re not careful. You’d be out the $25 if you hooked it up wrong. Hence, my reminder label on its cover.

But for $25 this one has variable settings to adjust for higher/lower heat output when using different thicknesses or doubling of the nickel strips used to connect the battery terminals together.

When you touch the two probes to the terminal strip to be welded, the controller can deliver either 1, 2, or 3 very quick pulses of high current whose duration can also be shortened or lengthened for the different heat settings. The settings are selected with the push buttons seen on the control board. Its duty cycle isn’t rated for steady production, but for home use, this has been great! And it doesn’t matter if the batteries are lithium, Nicd, etc.

Nicd battery packs may be somewhat simple with just the batteries and possibly a thermal sensor to monitor the heat buildup when charging or using the battery pack.

The lithium battery packs, however, most likely have their own BMS (Battery Maintenance System) contained on a small circuit board which gets connected properly into the battery pack while being put together. You might even be able to reuse the original from the weak pack you are rebuilding.

You can also buy a proper BMS for the actual battery pack being built. You’ll need to know the packs voltage, current rating, the # of cells in series/parallel, etc. It sounds more complicated than it really is. Plus, there are many “how to” videos and instructions online for various configurations to guide you.

Some pre planning and thinking before you start putting the pack together is needed. And be careful to keep the connections isolated and insulated where necessary. Allow for the connection leads from each battery cell to the appropriate connection point on the BMS being used.

Selecting the proper BMS will protect your battery pack from being over charged or discharged below its safe cut off voltage level. It will also monitor each individual cell for voltage and if there’s a problem it will open up the battery’s output circuitry. A simple BMS for a cordless drill, etc. might run in the $10 range +/-. The BMS for this 4-cell, 14.4 vdc pack pictured was under $10 delivered. Larger and more complicated battery packs might require more complicated and expensive BMS modules.

Here’s a pic of the mini spot welder with its welding leads and my car battery power supply. I used the bad battery pack cells (red) for trial spot welding to set the right heat settings on the device before welding the connection tabs to the new (blue) batteries. Pulling on the connection points with a pair of pliars left the welds on the battery terminal after ripping through the nickel tabs. A good weld.
IMG_1387.JPG IMG_1388.JPG IMG_1392.JPG IMG_1391.JPG

Make a drawing of how the pack you are rebuilding is laid out (copy the pack being replaced). Then once you have the heat setting selected, the order of connecting the batteries together properly, and the layout of the tabs for the wired connections to the BMS, it’s time to start spot welding those connections.

Here are some pics of the battery pack being made for the key programmer. And a pic of the purchased BMS and the spare battery pack being put together. The clear tape used is a high temperature tape made for this purpose and is readily available. The chart is a guide for choosing the proper size nickel strips for the connections based on the ampacity needed. The strips can also be doubled up(or more) for the ampacity required.

Finished.JPG BMS_A.JPG BMS_B.JPG Nickel Strip Current Capacity.jpg IMG_1393.JPG

In one of the pics you can see where I purchase my Lithium-ion batteries from. They also have other types, different amp hour ratings, brands, sizes, accessories, etc. at a most reasonable price and very reasonable shipping charges.

For a cost example: If the locksmith could have found a ready to buy replacement battery, he said it was in the $100+ price range. The replacement battery packs we built had twice the amp hour capacity vs the original. Each pack had 4 batteries at a cost of $28 per pack. The BMS were about $8 each with delivery. Each pack with double the capacity totaled $36 to build after the purchase price of $25 for the spot welder and a roll of that tape.

Now we’re using the welder to rebuild both of our cordless drills, flashlights, impact drivers, etc. battery packs. I may even rebuild my very old Makita drill’s 7.2 volt battery pack……if I can find it.

Now you can rebuild the old battery packs for your cordless grease guns.
 
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Russell King

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Thank you for posting this information. I was interested in doing this type of repair but had no idea how to get the batteries attached to each other.

One piece of information you did not provide is the name of the spot welder or where you bought it. Would you please provide that information also?
 
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jaxs

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Good post that can save people some bucks,not to mention not having to trash tools because they can't find replacement batteries for them.
I haven't used cordless tools on a regular basis for years but when I did I'd collect bad nicad batteries to salvage cells for rebuilding pacs. It's a good thing I never messed with a lithium-ion because I used one of those old fashion soldering irons with a tip larger than my thumb to stick metal strips to batteries.
 
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bird dogger

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Kubota B2650 and lots of other equipment
Feb 24, 2019
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North Dakota
Thank you for posting this information. I was interested in doing this type of repair but had no idea how to get the batteries attached to each other.

One piece of information you did not provide is the name of the spot welder or where you bought it. Would you please provide that information also?
Hey Russell,
Glad this post might be of value to you!! I was hesitant to post a direct link to the one I bought because most likely it would become invalid in a very short time. I purchased it off of Ebay. Here's a direct link to that one:
Diy Portable Mini Spot Welder Machine 8-24V Voltmeter for 18650 Lithium Battery for sale | eBay

If that link becomes useless, here's the ebay "search term" i used to find mine or very similar units:
On Ebay search for "DIY Portable Mini Spot Welder Machine 8-24V Voltmeter For 18650 Lithium Battery"

A Google search for: mini spot welder for batteries or another: mini spot welder for 18650 batteries
will get you other brands, types, videos, etc.

Amazon as well.

Search the same terms on youtube for all kinds of "how to" and "reviews" of different models, as well.

The high temp tape was found on Ebay with this search: " High Temp Tape, 5 Pack Multi – Sized 1/8”, 15/64”, 15/64”, 15/32”, 5/64”
This multi pack was about $18 and there's enough tape to last a couple of lifetimes.
You can also find single rolls or variants as well for less money shipped.

The BMS boards (Battery Maintenance System Protection) were found with a search like this:
Li-ion Lithium 18650 Battery BMS Charger PCB Protection Board
But again, you need to know the proper voltage, ampacity, etc. of your battery pack being built to purchase the correct BMS. A similar search on youtube will return lots of videos on the different types, features, building sequence, etc.

The BMS boards I purchased came with a small diagram with the proper electrical schematic for the hookups. Once you watch a few youtube videos its much easier to understand the hookups.

Once you get started and run into some questions.....post them and I'm sure we'll be able to help answer them. Or start a conversation as well.

The best starting advice: Draw on paper the battery layout for your battery pack build. With your proper BMS in hand: decide how you want it to be added to your pack for the easiest wiring hookups.
Make sure you allow for the additional tabs added between the batterys for the BMS wiring.
(I welded the BMS tabs to the Battery Connection Tabs first and then welded the connection tabs to the batterys themselves. ) Always mindful of keeping the terminals isolated to prevent short circuits.

The batterys being connected together must all be at the same voltage level. I used 3.0 volts as my guide. You may have to charge or discharge cells to get them all to an equal voltage. (A BMS requirement).

Study some "How To" tutorials online that will show up with the above searches before you begin your project. Once you understand them, you should be good to go.

Some welding practice on spent batterys (lithium, NiCd or even regular alkaline batterys) will get you proficient on the heat settings for your applications.

Hope this helps to answer some questions and helps you get started !!

David
 
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JimmyJazz

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B2601
Aug 8, 2020
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Pittsburgh, Pa
With some recent discussion about battery packs for our cordless tools and how expensive they are to replace, I thought I’d share what I had come up with to rebuild the battery packs for my cordless tools: A mini spot welder for lithium battery packs and other cordless tool packs. And if you are just a little bit tech savvy, willing to learn, careful with your planning, layout and building process, it’s not a complicated procedure. And the best part: it’s not expensive!

It started when my locksmith buddy said he had been unsuccessful finding a replacement battery pack for his portable key programmer that could operate from an internal Lithium-ion battery pack when no AC plug in was available (which happened quite often). The replacement packs were terribly expensive when they were available but everywhere he checked now the response was NLA (No longer available).

When he mentioned it to me, I suggested we just build his own battery pack and maybe a spare at the same time. He never thought that was possible. Since the lithium-ion battery is very heat sensitive, connections should not be soldered together unless you’re extremely quick! Instead, to make the connections a mini spot welder is used.

A commercial duty spot welder runs a few hundred dollars. But a portable mini spot welder that requires you to provide your own power supply (think 12vdc car battery) can be had in the $25 range. That’s what I paid for mine, including delivery.

You do have to be careful when using it, as there is no “reverse polarity” protection and you can fry the control board if you’re not careful. You’d be out the $25 if you hooked it up wrong. Hence, my reminder label on its cover.

But for $25 this one has variable settings to adjust for higher/lower heat output when using different thicknesses or doubling of the nickel strips used to connect the battery terminals together.

When you touch the two probes to the terminal strip to be welded, the controller can deliver either 1, 2, or 3 very quick pulses of high current whose duration can also be shortened or lengthened for the different heat settings. The settings are selected with the push buttons seen on the control board. Its duty cycle isn’t rated for steady production, but for home use, this has been great! And it doesn’t matter if the batteries are lithium, Nicd, etc.

Nicd battery packs may be somewhat simple with just the batteries and possibly a thermal sensor to monitor the heat buildup when charging or using the battery pack.

The lithium battery packs, however, most likely have their own BMS (Battery Maintenance System) contained on a small circuit board which gets connected properly into the battery pack while being put together. You might even be able to reuse the original from the weak pack you are rebuilding.

You can also buy a proper BMS for the actual battery pack being built. You’ll need to know the packs voltage, current rating, the # of cells in series/parallel, etc. It sounds more complicated than it really is. Plus, there are many “how to” videos and instructions online for various configurations to guide you.

Some pre planning and thinking before you start putting the pack together is needed. And be careful to keep the connections isolated and insulated where necessary. Allow for the connection leads from each battery cell to the appropriate connection point on the BMS being used.

Selecting the proper BMS will protect your battery pack from being over charged or discharged below its safe cut off voltage level. It will also monitor each individual cell for voltage and if there’s a problem it will open up the battery’s output circuitry. A simple BMS for a cordless drill, etc. might run in the $10 range +/-. The BMS for this 4-cell, 14.4 vdc pack pictured was under $10 delivered. Larger and more complicated battery packs might require more complicated and expensive BMS modules.

Here’s a pic of the mini spot welder with its welding leads and my car battery power supply. I used the bad battery pack cells (red) for trial spot welding to set the right heat settings on the device before welding the connection tabs to the new (blue) batteries. Pulling on the connection points with a pair of pliars left the welds on the battery terminal after ripping through the nickel tabs. A good weld.
View attachment 129557 View attachment 129556 View attachment 129558 View attachment 129559

Make a drawing of how the pack you are rebuilding is laid out (copy the pack being replaced). Then once you have the heat setting selected, the order of connecting the batteries together properly, and the layout of the tabs for the wired connections to the BMS, it’s time to start spot welding those connections.

Here are some pics of the battery pack being made for the key programmer. And a pic of the purchased BMS and the spare battery pack being put together. The clear tape used is a high temperature tape made for this purpose and is readily available. The chart is a guide for choosing the proper size nickel strips for the connections based on the ampacity needed. The strips can also be doubled up(or more) for the ampacity required.

View attachment 129562 View attachment 129560 View attachment 129561 View attachment 129564 View attachment 129563

In one of the pics you can see where I purchase my Lithium-ion batteries from. They also have other types, different amp hour ratings, brands, sizes, accessories, etc. at a most reasonable price and very reasonable shipping charges.

For a cost example: If the locksmith could have found a ready to buy replacement battery, he said it was in the $100+ price range. The replacement battery packs we built had twice the amp hour capacity vs the original. Each pack had 4 batteries at a cost of $28 per pack. The BMS were about $8 each with delivery. Each pack with double the capacity totaled $36 to build after the purchase price of $25 for the spot welder and a roll of that tape.

Now we’re using the welder to rebuild both of our cordless drills, flashlights, impact drivers, etc. battery packs. I may even rebuild my very old Makita drill’s 7.2 volt battery pack……if I can find it.

Now you can rebuild the old battery packs for your cordless grease guns.
I have seen this type of "MacGuyvering" on YouTube accompanied by firetrucks ,smoke and bewildered Chinese people sheepishly scrambling about . I like to ask myself what can go wrong . If the answer is potentially catastrophic I am out. Like getting a private pilots license . Just because you can does not mean you should. Risk/ reward/ liability......Good luck to you and your homeowners insurance company.
 
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bird dogger

Well-known member
Vendor Member

Equipment
Kubota B2650 and lots of other equipment
Feb 24, 2019
1,622
1,501
113
North Dakota
I have seen this type of "MacGuyvering" on YouTube accompanied by firetrucks ,smoke and bewildered Chinese people sheepishly scrambling about . I like to ask myself what can go wrong . If the answer is potentially catastrophic I am out. Like getting a private pilots license . Just because you can does not mean you should. Risk/ reward/ liability......Good luck to you and your homeowners insurance company.
One does have to know one's own capabilities and/or limitations. Most things are put together by humans.

There is really no rocket science involved in this procedure. Just some careful planning, safety precautions, and building practices. I don't think it qualifies as "MacGuyvering" as absolutely no shortcuts or substitutes are being used, no safety precautions tossed out, etc. In fact the opposite.

As a retired technican with 40+ yrs experience in the similar fields, I have complete confidence in the batterys I put together. When finished, they are of better battery quality, BMS quality, and build quality than the packs that come out of the mass produced cordless tools, etc.

Even this very expensive original pack from this key programming machine was of questionable build and quality. Probable why it failed so early and was no longer available.

I do agree with you though, that if you don't understand the process and the precautions necessary to make a quality battery pack....you should not be doing it.

But that can be said for everything tractor related, car related, welding, appliance repair, boating, hunting, fishing, baseball, motorcycles, skydiving, scuba diving, mowing your yard, etc. Anything in life can kill you once you get out of bed. Even if you stay in bed all your life....it will kill you and the ambulance and firetrucks will still come to your house.

But at least this way, one knows how you built the pack and with what quality items you built it with vs a cheap off the shelf tool or in fact any factory purchased cordless tool.

You have to decide for yourself what you are capable of and the potential risk to reward of any venture one takes. :)
 
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