Can't find a replacement battery for an old cordless drill? Here's how to adapt a different battery to an old drill giving it a new lease in life.




New Life for an Old Drill

I don't like to waste. In fact, it pains me to see perfectly good items thrown away; a not so uncommon sight in our consumer-driven society. Furthermore, the "thinkerer" in me always wants to see if something can be fixed; I appreciate the challenge. So it should be no surprise that when I saw a good quality drill being sold for almost nothing (Figure 1), I bought it.  This is a very nice, two-speed,  BOSCH 13.2V drill with almost no signs of wear. The seller told me he could not get replacement batteries for it. A quick search through the web confirmed the owner's assertion. It's really hard to get replacement batteries for it, and even if you could, they probably would be expensive. Most people just opt to get another drill, new batteries and all. But I had a different plan...

 Figure 1 - The Drill

The Semi-Cordless Drill


A cordless drill is a nice tool in that you don't need to be near an outlet to operate it. However, I'm not particularly fond of these "gigantic" batteries some drills carry these days. These are bulky batteries and make the tool heavy and hard to maneuver. So it occurred to me that I could just sever the physical connection from the battery to the drill. In other words, I would connect the drill to a replacement battery though a cord. I call this the "Semi-Cordless Arrangement" and is shown in Figure 2. This strategy opens the door for using all sorts of replacement batteries, not necessarily the (expensive) original manufacturer's batteries. I often prefer this arrangement since it makes the tool lighter. As an added advantage, you can often use higher voltage batteries, thus increasing the power available to the device. Let's now see how this was done.


Figure 2- The Final Arrangement


The Conversion Process

First a word of caution. These Batteries, though not very high in voltage, can deliver huge amounts of current. If you decide to make a mod like this one, be sure to avoid accidental short-circuits as there is a danger of fire. While I was doing this, I accidentally shorted the battery with my multimeter and saw some serious sparks flying. Be careful around these batteries! That said, the procedure is quite straightforward. If you can use an Electronics soldering iron, you can do this.

The first step was selecting a replacement battery. Since I wanted to keep things inexpensive, I headed to the Harbor Freight store where I knew that brand-new 18V NiCd rechargeable batteries can be had for $15 (Figure 3). There's no guarantee that your drill, designed for 13.2V will work reliably with 18V. However, my experience has shown that, for good quality ones, the design has enough margin to support the higher voltage. In fact, I've done another conversion where the original drill was designed for an even lower voltage. After more than a year of use, I haven't had any issue. That said, there is no guarantee here. Your best bet is to buy a drill from a good brand as chances are the design (and even the mechanical parts) will stand a better change of operating reliably at the higher voltages. As we will see further down, the higher voltage also results in higher power and higher rpm speeds. This can be an advantage for some practical uses.



Figure 3 - The Battery

The next decision was to determine the type of cable to use to connect the battery to the drill. These motors draw a considerable amount of current, so you want to use a thick cable to reduce losses. I decided to use a $1 store extension cable, normally used for AC connections but re-purposed here for a DC connection. This cable is thick, long enough for my uses, and by marking the polarity on the cable can be used with a DC source with no problems (Figure 4).


Figure 4 - The Cable

Start by cutting the plug end of the cable and soldering it directly to the battery terminals (be careful not to short the plug accidentally!). I used heat-shrink tubing to further isolate the connection. See Figures 5 and 6.



 Figure 5 - LED current

Make sure to identify the positive and negative terminals with a multimeter and mark them on the plug. This will avoid mistakes when connecting to the drill.



Figure 6 - The Battery Connector

Since the drill came with no battery, I built a "base plate" to cover the bottom of the handle. This base can be made of any material you have handy: metal, plastic, perhaps even wood. I thought it would be cool to also re-purpose and old pcb board I had laying around. After all, the name of the game here is "recycling". Figure 7 shows how I marked the outline in the pcb (using a Sharpies marker).


Figure 7 - Marking the "Base Plate" outline.

 Using a saw and a dremel rotary tool, I cut the pcb and perfected the outline. See Figure 8.


Figure 8 - The Base Plate

Next, I drilled some holes though the plate and the drill base. One big hole for the cord, and three small holes to fasten the plate to the drill. I found a nice rubber "pass-through" tube that protects the cable as it passes through the plate. The complete assembly is shown in Figure 9.  



Figure 9 - Plate and Cable

Finally, I simply soldered the cable directly to the input terminals inside the drill and protected them with heat-shrink tubing (Figure 10). Be sure to identify which is the positive and which is the negative terminal *before* soldering.


Figure 10 - Soldering at the Drill End


Figure 11 shows again the final result. Notice how I marked the positive terminal to avoid polarity swapping. While the drill I have seems to tolerate a polarity inversion (yes I tried it by accident...) there's no guarantee yours will, so better be safe than sorrow! Notice also that I used two long screws and nuts to affix the "base-plate", plus a plastic "zip-tie" on the other end. This arrangement is easy to disassemble should I ever need to fix something inside in the future. 

At this stage you might ask how do I charge the battery? This is the reason why I made the male+female plug arrangement rather than soldering both ends directly. This way, I can disconnect the battery and connect it to a standard 18V charger. Harbor Freight also sells 18V NiCd chargers, but I already had one for some other 18V tools I own. I simply use crocodile cables to connect the plug to the charger and it works fine.

How does the drill perform?  I'm pleased to report it works very well! The 18V "upgrade" really gave it a substantial power increase. The rpm speed also increased a bit (see this other article for an explanation of how o measure rpms). The maximum rotation speed went from 1200 rpm at 13,2V to about 2000 rpm at 18V. This is a substantial increase.



Figure 11 - The Final arrangement

So, in summary, for a modest total "investment" of about $20, I have a fully functional, quality drill that should last me a long time. And I have the satisfaction of knowing I "saved" this one form a certain landfill destiny. It was a good day in my book:)

Comments, questions, suggestions? You can reach me at: contact (at sign) paulorenato (dot) com