How to Rebuild Cordless Drill Battery Packs

A picture of Lithium Ion battery used in Dewalt Cordless Drill

If you were to name one common piece of equipment in every DIYer’s arsenal of tools, I bet a cordless drill will cross your mind. Home repairs tend to be endless and inescapable. With a cordless drill in your reach, it will always save the day.  

Battery troubles will, however, limit the usefulness of a cordless drill. Typically, the drill battery pack gives in to age and goes kaput. Subsequently, rebuilding the battery pack is an economical and dependable remedy to such an issue.

On that account, let’s delve into the discussion of how to rebuild cordless drill battery packs.

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How to rebuild cordless drill battery packs

Once the battery pack of your cordless drill bites the dust, there are several things you can do. Seeking replacement batteries sounds like a good idea until you realize they are pretty expensive or even hard to find. You can also opt to relinquish the whole tool and label it as of no service to you.

The better way to get your favorite power tool back in action is to rebuild its battery packs. Rebuilding means replacing the pack’s weak or dead rechargeable battery cells with new hi-capacity cells. The practice reconditions the battery packs to new strengths that enable your cordless drill to go the distance.

Rebuilding battery packs tend to be a widespread practice among contractors and DIYers since it is pocket-friendly and delivers a higher power rating for the rebuilt battery than the original batteries. Further below is a stepwise process elaborating how you can carry out this remedy.

Pre-rebuilding preparation

This is the step that you equip yourself with all the tools and materials necessary for rebuilding. Here’s a list of the necessities to get you started;

  • Wire and tape
  • Rosin-core solder
  • New replacement battery cells
  • A hot melt glue gun
  • A soldering iron
  • Spring clamps 
  • 4-in-1 screwdriver

When choosing new cells for battery rebuild, you have to be explicit with your choice. For clarification, you can obtain one of the original cells by unscrewing and pulling the pack’s top off. What you need to do is to obtain the essential cell specs. 

Start by taking measurements of the single cell. Typically, most cordless drills use Sub C size cells. Taking note of the mAh rating of the dead batteries is of the essence. If you wish to obtain more details of the old batteries, you can look them up online.

The information you obtain from the above should guide you when purchasing new cells. The baseline is, settle for cells with a discharge rating of 5C or above. You can also choose cells with a higher mAh rating than the original ones, provided you are ready to spend more.

Another momentous consideration when procuring new cells is the design. It is highly recommendable to choose those with the tabs already welded in place. That said, let’s get right onto the actual rebuilding as discussed below.

Layout and glue

Start by prying the battery pack open. The original battery pack should serve as a template by providing a layout to follow when arranging the new cells. It would be best to place the original battery pack on a piece of paper and trace its outline with a marker for reference purposes.

Make markings of the position of the terminals (both the negative and positive terminals) on the drawn outline. Arrange the new cells on the trace on a flat surface corresponding to the markings.

Using the old pack as a guide (follow its pattern), lay out the polarity and solder tabs in a likewise direction. Employ a hot-melt glue gun to glue the cells together. 


With the cells glued together in a pattern similar to that of the old pack, it is time to solder all the connections. For safety reasons, you should clamp a heat sink onto the tabs before introducing heat to protect the battery.

Then, use a rosin-core solder to solder the tabs together. Repeat this process with the extra rows/groups of cells. Remember to carry out soldering in a meticulous way for a perfect outcome.

Original terminals and circuits transfer

The transfer is carried out by disintegrating the original terminals from the original pack and soldering them on the new pack, respectively. Also, the insulators and the temperature sensors from the old pack should be transferred and set up in the plastic case.

Complete the rebuilding

You are almost through. Set up the rebuilt battery pack in the casing. It should sit in without a hassle since the layout is similar to that of the older pack. Re-fix the terminals into their respective positions on the casing and close the plastic case. Remember to charge it and test it out. It should turn out excellent.  

How to rebuild 18V battery

A battery pack that can pack a punch is greatly preferred for most cordless power tools. This makes the rechargeable battery pack with a voltage rating of 18V quite the ideal option. However, despite conveying immense power, the pack is still prone to becoming defunct due to exhausted charge cycles or other reasons.

It has by now been established that rebuilding is a very practical remedy when you have battery issues. Therefore, you should consider rebuilding when you can no longer get the juice from your 18V battery pack. To start with, let’s have a look at some of the materials you need. They include;

  • Copper strips and utility knife
  • Screwdriver set
  • Solder and soldering iron
  • Tin snips, battery tester
  • 1/2” foam board
  • 12, 1.5-volt batteries

Typically, a set of 12, 1.5-volt rechargeable batteries makes up the 18V pack. The connection between the batteries is through soldering, whereby a positive terminal of one battery links to the negative terminal of another battery. Battery rebuilding in this context is by the replacement of single inoperative batteries. Enough of that; let’s look at the steps to follow when rebuilding the 18V battery pack.

Deconstruct the pack

Start by disengaging the battery pack from the power tool itself. Dismantle the casing into its two sections after unscrewing with a screwdriver. Check for the terminal plug represented by two metal strips located in the slot where the tool slips in to contact the battery pack.

Once identified, detach the wires connected to the negative and positive electrodes. Lift the collection of small batteries from the bottom to isolate them from the casing. Take note of the circuit connection of the old battery using a felt tip marker.

It is advisable to use denotations to keep a trace of the circuit flow. Please start with the battery connected with the positive terminal of the terminal plug and label it as battery A. On the pack’s underside, check for the battery connected to the bottom of battery A and mark it as battery B.

Keep track of the old pack’s flow while labeling until it ends at the battery linked to the negative terminal electrode. The denotations will end with the battery attached to the negative terminal plug as battery L with the typical twelve batteries.

Create a template

You will need a template to serve as a reference when rebuilding the battery pack afresh. By cutting with a utility knife, obtain a piece of ½” thick foam board that will serve as a template.

Now, trace an outline of the old battery pack on the board. With the old pack as your guide, make positive and negative markings on the foam board at the spot where batteries were connected to both terminals of the terminal plug.

Layout the new batteries

Using the earlier denotations as a reference, install a new battery into the slot corresponding to battery A as per the template and label it as battery A. The terminal should face upwards.

This is followed by installing another new battery into the slot corresponding to battery L. You should install it with the negative end facing up and label it battery L. You have almost ten new batteries remaining. Label them with the letters between A and L, i.e., begin with B and mark all the way to K.

Install the ten labeled new batteries into their exact spot of the template while ensuring that the terminals match the sequence letter of the batteries in the old pack.

Re-fix the new cluster into the casing

Having followed the denotations correctly, your new cluster of batteries should assume the arrangement of the original one. To join the new batteries fixed in the foam board, tape them together. Proceed to fix the new cluster in the casing of the battery pack.

Reconnect the terminals

To complete the circuit, you will need to link the terminals correctly. Using the old pack as a guide point, solder copper strips across the terminals of the new cluster appropriately.

The subsequent step will be to join the battery terminals with the pack’s terminal plug. Identify the positives and negatives. You create a connection by soldering two wires arising from the open negative and open positive individually. You will then solder each wire to the battery pack’s respective negative and positive terminal plug. 

Finalize rebuilding

Fix the new rebuild battery pack into the correct position at the bottom of the case. Join the two sections of the case back together and reinstall the screws. If you reach this part of the process, your battery pack is as good as new!

The video below shows how to rebuild cordless drill battery packs. Listen to it and follow the process for visual guidance.

How do you wire a battery without soldering?

For a battery to power a tool/device, wiring the battery is ineliminable in order to re-establish the circuit(connection). Soldering is one way to effectuate the wiring. However, this method is advised against since it compromises the battery’s internal chemistry through the introduction of heat.

Therefore, the heat produced from soldering will damage most batteries, including NiMH and NiCad batteries. Soldering also poses a safety concern for you. With all these implications in play, how then can you wire a battery without soldering?

You can use battery holders to wire the battery. The downside to this option is the inadequacy of space that can limit the battery holder. Alternately, you can use spot welding to wire a battery. This option is recommended for batteries lacking solder tabs and creates a permanent link to the battery.

You apply the welding electrodes to the top of the tab and position them closely. The contact and battery terminal get pressed together to create a connection that results in zapping by discharging a capacitor. 

The zap gets both parts heated to some extent to facilitate the melting and binding of some little metal. This is effective since it yields low total energy and adequate temperatures that spread appropriately before contacting sensitive battery parts.

Frequently Asked Questions -FAQs

Can lithium-ion battery packs be rebuilt?

Yes, they can. However, one needs to take extra care and pay special attention when rebuilding or reconditioning Li-ion batteries. This is because of the safety concerns involved. Li-ion battery cells are pressurized and contain electrolyte as an internal component which is flammable. It is advisable to enact precautions such as eye protection glasses.

Other concerns like the vulnerability of internal safety circuits, high costs of these batteries, and limitations in shipping Lithium-ion batteries (especially by air) make rebuilding Li-ion battery packs quite uncommon. 

How do you weld battery tabs?

The spot welding technique is applicable in welding tabs or strips onto batteries. TIG battery welding process can also generate adequate temperatures for welding tabs. This process has the advantage of producing localized heat without contact.

Laser technology is also excellent for welding tabs to the terminals for batteries. The differences in battery configurations and sizes influence laser technology.

Can I solder a lithium battery?

It is possible to solder lithium batteries. However, it can be a pretty dangerous endeavor since excess heat can result in the explosion of the battery. Something to keep in mind is you ought to remember not to solder/weld the wire directly on the polarity of the battery. Also, use high-quality solder bearing flux core.

Cost to rebuild DeWalt 18v battery

It would cost you $39-$40 to procure the 18V NiCaD rechargeable battery rebuild kit from the DeWalt brand. The price may vary to even about $32 for about 15 cells which are enough for one full 18V battery pack in online marketplaces like Amazon. If you seek professional help in rebuilding, you will have to add labor costs besides incurring costs of new batteries.


Out of the numerous power tools, a cordless drill stands as a must-have tool for most households due to its unparalleled handiness. Being a favorite for DIYers and professionals, it is one of the most used power tools, and because of this, its battery life gets compromised in the long run.

As accentuated in this article, battery rebuilding is one of the most cost-effective and exceptional ways of salvaging a battery pack that no longer holds a charge or is simply dead. Even better, rebuilding the battery pack for your cordless drill is a project you can achieve by yourself, as guided in this article. Of importance is to remember the safety considerations highlighted in this article, especially when dealing with li-ion batteries.

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