Cordless Tool Batteries - A Primer

Just Looking for Power Tool Batteries?

We sell them. Get to the battery you need. (I only put this here, because I noticed a lot of people were finding this article, when they were simply looking for a battery.)

The Basics

Power tool batteries are made up by taking several lower voltage cells and hooking them together in series. Each cell has the same rating in Amp hours (a measure of how much electricity flows through a circuit in one hour with a flow rate of 1 ampere). So an 18v tool might have 12 cells at rated at 1.5 volts and 2.4 Amp hours, which would produce an 2.4Ah 18 volt battery.

Almost all of the cordless tools on the market today use one of the following three battery technologies:

• NiCad / NiCd (Nickel Cadmium) - Nickel Cadmium batteries are commonly found in tools from Dewalt, Bosch, Porter Cable, Milwaukee, Skil and Hitachi. Advantages and disadvantages of NiCad are:

• Least expensive cell technology
  
• Has the least temperature sensitivity of the three battery types
• A large number of charge cycles is possible
  
• Stored batteries quickly lose charge
• Can develop a sort of "memory effect" (see the below section on memory) if not regularly drained and fully charged (sometimes referred to as conditioning)
• Cadmium is a heavy metal and is considered an environmental hazard
  

• NiMH (Nickel Metal Hydride) - Nickel Metal Hydride batteries are used extensively by Makita and Panasonic. The advantages and disadvantages of NiMH batteries are:

• Much higher potential capacity than NiCad batteries
• Requires less conditioning than NiCad
• While you still shouldn't just toss a NiMH battery, it is considerably less toxic than a NiCad
• Much more sensitive to temperature than NiCad
• Some studies show that the battery performs less reliably after repeated empty to full charges
• Loses a charge more quickly than NiCad
  

• Li-ion (Lithium Ion) - Lithium Ion are relatively new to the power tool industry. Lines using them have been launched by Milwaukee (the 28 Volt V28 Tools) and Makita (The 18 Volt LXT Line). In addition, Dremel makes a lithium ion rotary tool, which was the first lithium ion tool we carried. We expect to see more tools in this category soon, as Bosch has announced 10.8 volt and 36 volt tools and Dewalt is also jumping into the 36 volt waters. Others have been dropping hints as well. Lithium ion is relatively new in power tools, but some general advantages and disadvantages of lithium ion cells are:

• Much higher capacity than even NiMH
• Charge loss during storage is less than half that of NiCad
• No memory at all, no periodic conditioning is needed
• From the early reports we are hearing on the Makita and Milwaukee units, lithium ion seem at least as temperature sensitive as NiMH
• The charging process is much more complicated from a technology standpoint, meaning more expensive chargers or batteries (depending on the manufacturing choices)
• The battery manufacturing cost is substantially higher

So Why are Power Tool Batteries so Expensive?

From time to time I hear someone complain about the price of tool batteries, although thanks to a few of our power tool manufacturers coming out with battery 2-packs, I've been hearing less of that particular complaint. But the idea behind the complaint is that I can go out and buy a 12 pack of AA batteries for under $8. That is 12 cells x 1.5 volts, or 18 volts total.

Of course, this point of view requires you to forget that your standard alkaline batteries are not rechargeable. So if you get 400+ charge cycles out of a cordless tool battery, then that $8 18 volt battery suddenly costs you $3,200. That is not even taking into account current draw and other issues that would make a AA cell less than ideal for the purpose.

The costs in rechargeable batteries also are influenced by the makeup of the battery. NiCad, NiMH and Li-Ion are all much more expensive per cell than a lead-acid or alkaline cell. In addition, there are costs in designing the packaging, wiring the cells and otherwise making it work safely and effectively in a power tool.

Memory

Voltage depression is the technical name for what people commonly refer to as memory in Nickel-Cadmium or Nickel Metal-Hydride batteries. While NiCad and NiMH are both capable of developing voltage depression, it is less likely with power tools than with low amp draw items like laptops or cordless phones. The effect is caused when the cells in a battery are drained to the same level at the same speed frequently. To quote a Makita training pamphlet on batteries:

This does not happen with tools in industrial applications due to the fact that tools are used in various applications. For instance, sometimes a battery will be used in a high current draw application such as installing large lag screws and other times in a low current draw application such as installing deck screws. The changes in draw and the rate of discharge prevent memory from occurring.

The voltage depression is actually caused by crystalline structures forming on the nickel plate (on both NiMH and NiCad) and the Cadmium plate (on NiCad). The larger the crystals become, the less energy your battery can produce.

The Amp hour (Ah) Rating

I gave the technical definition of an Amp hour above. Now, I'm going to actually explain what that means to you. If you had a 9.6 volt battery rated at 1.3Ah and another 9.6 volt battery rated at 2.6Ah, the 2.6Ah could power the same tool doing the same job two times as long. The best metaphor for the Ah rating is the gas tank on a car. Depending on how you drive a car, if you maintain it and the engine that is in it, your mileage will vary widely, but you'll always go farther if you have a bigger gas tank if all the other factors are the same.

A Great Resource to Learn About Batteries

I stumbled across a site a couple weeks ago, and using my existing knowledge and some information I picked up there, I wrote this little primer. However, I recommend everyone should go to Battery University to learn from the real experts. Their information is not specific to power tool batteries, but much of the material applies equally to all types of batteries.

Any Questions?

If anyone out there has any questions, I'll do what I can to answer them, or in other words, yes I take requests.

Matt Griffith

What's an amp worth?

After having training from a few of the major power tool companies in the world, I've learned a few dirty little secrets of the power tool industry. Today, for Christmas, I'll share the big one!

You know that amp rating that so many consumers use to determine how much {insert manly growl} power a tool has? It really means very little. The rating process is kind of silly. The testing labs get a tool from a manufacturer and are told "We would like to be rated for 12.0 amps". The testing lab then puts heat sensors in certain areas of the tool, and then apply the requested current to the tool... as long as the sensors do not get above a set temperature in a set amount of time, then the lab says "Hey this is a 12.0 amp tool!"

Sure, the tool can operate at 12 peak amps, but is it using that power effectively? Is it transferring the energy it is producing to the work piece or is it simply shaking the tool out of your hands? I have seen tools that have a lower amp rating out-perform high amp tools on a regular basis.

In addition to the question about efficiency, the next one you should ask is how many amps is your circuit rated? Many outlets are only rated at 15 amps, and if you are running the wrong tools at the same time, you'll be replacing a fuse, resetting a breaker or worse an outlet. This could be a real issue if you are in the middle of a cut on one of your last pieces of material, or if the circuit panel is hard to get to.

So then, how do you select a tool if you cannot go by amps? That gets a little harder. The United States is very amp oriented, this amp dependence has been driven by the marketing departments for several of the power tool companies. Many of them have no interest in educating their customers, so it is up to the people who deal directly with the customers. My suggestions would be to look at the other specs provided by the manufacturer. On a reciprocating saw, for example, look at the strokes per minute (SPM), the length of stroke, the amperage, whether it has orbital action and the weight. Using all of these, you can make a better determination whether or not it is the saw for you. The no-load strokes per minute (meaning they count it while the tool is not making contact with any work material) and the stroke length (the total distance the blade actually travels on each cut) determine how quickly a tool can cut. If you are cutting mainly wood, the orbital action simulates the action of a hand saw and cuts wood even faster. The amperage isn't entirely worthless, within one brand of power tools the amperage will show the relative power of this saw compared to the manufacturers other tools. The weight, while it isn't an indication of power, is really important... consider this, would you rather spend 30 minutes holding a 8 lb tool over your head or 28 minutes with a 10-1/2 lb tool? A few more insights on the wonderful world of reciprocating saws can be found on Brian Mark's blog entry from 12/24/2005.

The key to being happy with a power tool is to pick one that meets or just slightly exceeds your needs. By going for the tool with the most power, many people are also going for the tool that costs them the most and wears them out the fastest.

Make a list of the things you do with this type of tool regularly, the things you do relatively rarely and the things you might want to do from time to time. Once you have a list, decide how important it is that the tool you are buying does each one of these. Weigh those items versus fatigue caused by weight, the availability of power and any other special features that could be important to what you intend to do. Then with those considerations in mind, look at the tools and try to match the specifications to your profile of the "perfect" tool. Once you find it, order it.

Almost every major manufacturer of power tools offers at least a 30 day satisfaction guarantee (and usually not the case with air tool manufacturers, strangely). Don't be afraid to use the tool like you will be using it in the field. If it doesn't perform well, you can send it back under the terms of their guarantee. Yes, you will usually have to pay to send an unsatisfactory tool back, but isn't it worth $10 to get the right tool?

Well, I have to be with the family in 10 hours, so off to bed I go. Merry Christmas to all!
Matt G.

News from slightly behind the frontlines...

It was just a year ago when I was answering the phone calls of the last minute Christmas shoppers. I had already earned my present title, Director of Information Technology, but we were still getting our call center staff trained and up to speed, and I still had (have) an awful lot of knowledge about power tools kicking around in my brain (the kicking was mostly harmless). This year, I can gladly say I didn't have to take any phone calls, but knowledge is still valuable, and even asked for on occassion.

Looking back now, it is hard to believe we are the same company as when I started here 4-1/2 years ago. Back then, I did all of the customer service, product maintenance and the like single-handedly. I remember when we had a goal of an order an hour. That certainly has changed. As ToolBarn.com and ToolPartsDirect.com have grown and matured, so has our staff and our back-end technology.

In this, my inaugural blog posting (inblogural?), I just wanted to acknowledge the fact that without all of the people here stepping up to do their best, I'd probably still have to be answering phone calls while trying to keep our various systems up and running. In my estimation, that is one heck of a good Christmas present... Thanks everyone!

Tune in next time, when Matt shares his thoughts on ... hmmm, we'll I guess we'll all find out together.

Thanks for reading,
Matt G.