Introduction: Replace/Upgrade/Repair Power Tool Batteries - SAVE 50% or More!

This Inscrutable will show you how to replace the internal batteries of a cordless power pack.  I will also help you determine what batteries you need.

My cordless drill has been sitting on the shelf, useless, because the batteries are dead.  Not anymore...I replaced the internal batteries with ones that were a higher quality and longer lasting!  Others have suggested zapping NiCad batteries with high current...this may work, but also runs the risk of damaging any internal circuitry the battery may have, and could cause the batteries to explode and spray hot/toxic chemicals over you!  It's also only a short term solution.  This is a safer method with a guaranteed outcome, and a great upgrade.  If you're on a very tight budget and have shorted NiCd cells, you can isolate the bad cells with a multimeter and just replace the bad individual cells.

1) Soldering equipment
2) Small heat shrink tubing (optional, if your battery pack requires splicing)
3) Large heat shrink tubing (optional, if your battery pack has a temp sensor)
4) Correct screwdriver bits for disassembling the battery case
5) New replacement batteries (see step 2 for help)

In theory this can be done to just about any item that uses rechargeable batteries, but results may vary depending on many factors.  Do not attempt this unless you are confident soldering and working with high power electrical circuitry - many of these batteries pack a mean punch, especially when assembled!  NOTE: they carry enough current to weld in some cases.  In this example I will be using the battery from a Craftsman Professional 9.6v Cordless Drill, item # 9614 or 11030.

NOTE:  This was the first time I've used a very old camera and I did not realize that the pictures were not great until after the project was over...please let me know if you need more pictures or info!

Step 1: Is Your Battery Pack a Candidate?

Whether or not your battery can be used for this depends on two things:
1) How easy your battery pack is to open up
2) How ambitious you are in opening up your battery pack

I have seen three basic types of battery cases so far:

The easiest are assembled with standard screws...nothing special there!

To make things more difficult my battery pack used special security torx bits.  A cheap security bit set at Ace Hardware contained the bits I needed.  Here is the $3 bit set available online for $3.

The hardest type would be a battery case that is not screwed but glued together (for example, my laptop battery...which I'm debating doing this to)...some of these were never designed to be disassembled and you may break it in the process!  I suggest that you do not attempt to open one of these up unless you could see a way to get it apart cleanly, were desperate to upgrade, or about to throw it in the trash...basically you need to be willing to risk destroying the case.  You may be able to re-assemble without any signs that you've taken it apart, or you may damage the case beyond'll have to be the judge.

Step 2: Determine Type, and Buy Replacement Batteries

There are a few things you need to know about the battery:

1) Size
2) Capacity
3) Type
4) Voltage

I was lucky to have Panasonic batteries that were labeled with an item #.  Using that item # I was able to find all the details about the battery.  You may not be so lucky!  If you get stuck, see below for how you can find out your information.  If you have any doubts just use a battery with the same specs, however, you don't have to replace the battery with an identical replacement and you can easily upgrade in many cases.  Here is a breakdown of what I had to work with:

1) Size - 4/5 Sub C (aka "SC")
2) Capacity - 1200 mah
3) Type - NiCad (Nickel Cadnium)
4) Voltage - 1.2v

Typically you won't be able to use a different sized battery because of space limitations...but you could if you chose carefully.  If you can't find the details, you can measure the battery and determine the size by searching online based on measurements.  In my case there was a spacer under the pack that allowed the manufacturer to use the 4/5 Sub C instead of the full size Sub C.  They did this because the 4/5 Sub C battery is much cheaper than a full size Sub C.  I could have taken out the spacer and used a full size, but I was not desperate for more capacity and I liked the idea of saving money!

If you are unsure, get the same.  However, you can easily upgrade here!  This is a measurement of how much energy the battery can store (not how fast the energy is released...that's voltage!).  In my case, a 2400 mah battery would last twice as long as the 1200 mah battery.  The more mah, the more money you will spend.  Because I was fairly happy with the performance and I didn't want to spend a lot of money, I went with a nice compromise - a mild upgrade of 2000 mah.  However, if I was willing to spend more, I could have purchased batteries with more than three times the original capacity!  If you don't know your current capacity, there are ways to calculate it based on the output of your charger and the amount of time your batteries take to charge...upgrades are pretty cheap though so I won't go into details here.

Typically you will have NiMh, or NiCad, but there are many others, like Lithium Ion.  My batteries were NiCad, which have an undesirable property of having something called 'memory' (Otherwise, they are a very good battery for use in Power Tools because they can charge fast and are powerful).  NiCad batteries can't handle nearly the same capacity as NiMh, but they don't last as long.  In short, I felt that NiMh was a good choice for my application...but it may not be the best option for your application.  More NiMh/NiCad battery info.  You should consider your situation and determine if switching battery types is an upgrade for you.  If in doubt, replace your batteries with the same type.  

UPDATE ON MY NiMh CHOICE AFTER A YEAR OR SO OF USE: When I started this I liked the idea of a less-powerful battery that lasts longer.  In effect what I've done is made the drill 'weaker' in exchange for longer battery life.
1) I like the longer life...for smaller jobs it does what I need it do do and is usually available without needing to charge
2) I don't like the lower power.  I overlooked that I do occasionally use this for a heavy-duty job.  I still get by, but the battery needs to be fully charged or it really struggles to finish the job.
In conclusion, if I really was using this only for smaller jobs the NiMh would be great, but being able to power through heavier jobs is something that I realize now I took for granted.  It's like an economy car with a weak engine...but sometimes you want a big V8 :)  Of course, the specific drill you are using will make a big difference also.  If I need new batteries again, I think I'd be willing to spend  more money for higher-capacity NiCad's (greater mah) even if they had a shorter life, unless I was certain I was only using the drill for light-medium duty jobs (this is the only drill I have).  An example of the type of heavy duty job this struggles with: driving a #14 screw designed for use without a pilot hole...even with a fresh charge the drill is heavily burdened.

This matters a lot!  If you're an electronics whiz you may be able to determine that you can get away with a different voltage, but for the rest of us the safe bet is just to stay with the exact same voltage.  If the batteries aren't labeled you can do the my case I have a 9.6 volt pack that uses 8 9.6 / 8 = 1.2 volts per battery cell.

I found a ton of places online, but ultimately I chose  I was happy with the purchase and would recommend them if you don't want to bother shopping around on your own.  I purchased Tenergy batteries from them, which is a solid brand.  I also chose the option "With Tabs" and I would highly recommend this...I have made battery packs without tabs in the past and it is MUCH harder without the tabls.  The tabs shipped with a protective heat-shrink on was easy to remove before soldering.

Step 3: Replace the Batteries

In my case this was a very simple process after the battery case was removed:

1) Disconnect connections on old battery pack

2) Cut heat shrink around one battery that held the heat sensor against the battery (yours may not have this).  In my case, I think the heat sensor is there to monitor battery temperature and to limit current if the batteries get to hot (this is because heat damages batteries)

3) Remove the old battery pack.  Mine just lifted away without any other connections or tie downs.

4) Using the old pack as a reference, make an exact copy with the new batteries.  NOTE: I
used to assemble battery packs for R/C cars...those same instructions would apply here!  In short, use a hot iron but only for a very short time.  Too much heat can damage the batteries and could even cause them to explode...using the "tabs" option greatly reduces risk of battery damage and makes things go much faster. 

I found the easiest way to solder these tabs was the following: Smear a small amount of flux where the tabs would be contacting each other, place solder between the two tabs (I just held the tip of the solder between the tabs), and heat the top tab, compressing everything together.  Once all is hot, move the iron away from the connection so you can still apply pressure to the joint while the solder sets.  In one fell swoop the iron melted the solder and made a great tinning was necessary!  It took only a few seconds to make each of the connections. 

Aside from taking the heat much faster, the tabs were long enough that I was able to fold them backwards or sideways and connect to the neighboring battery (I had one tab pointing toward the neighboring battery, and the other tab pointing away...the tab that pointed away was folded back onto the first.).  The process is a bit harder without the pre-installed tabs...this is because it is more difficult to solder directly to batteries (because the battery acts as a giant sink and sucks the heat away before you can make a connection).

5) Installation is the reverse of removal.  I used a large heat-shrink tube to re-attach the sensor, but tape might work, and you might not have a sensor.  I was lucky in that the tabs were the same size as the quick disconnects, just not as thick.  I pinched the quick disconnect to be sure I had a solid connection.  I could have also re-used the heavier tabs from the other battery pack.

6) RECYCLE YOUR USED BATTERIES!  Did you know it's illegal in many places to throw away your old rechargeable batteries?  Recycling is free and easy, and you won't be dumping poison into the environment.  You'll be amazed how many places take used batteries:  CLICK HERE TO FIND A RECYCLER USING YOUR ZIP CODE -

That's it!  Note that it will take longer to charge if you upgraded to a higher capacity (ie: twice the run-time means twice the charge-time).  Let's review at what was accomplished:
1) Took a dead battery back and gave it new life, saving it from landfill
2) Upgraded the batteries to have a 66% greater capacity, and no memory.
3) Saved about 50% compared the cost of a pre-assembled replacement battery

In short: I was able to repair my batteries AND upgrade for about half the cost of a replacement.  NOTE: If I went with an identical replacement battery it would have only cost about 30% of a replacement power pack!  Not bad for less than an hour of effort per battery pack.

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