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© Copyright 2006 Work-4 Projects Ltd.

Cordless: where is it going?

By Jon Eakes

Not so long ago, I wrote in this magazine that the only real changes in cordless technology were the chargers, but that has changed. Today we can barely keep up with the cordless revolution because it has become the cutting edge of competition between the tool manufacturers: you buy a battery and you marry a brand name.
One of the biggest problems with cordless tools is the added weight. Although DC motors are lighter than AC motors, the battery still dominates the weight of the tool. In fact, overall weight is what limited the power of cordless tools to a maximum of 18 volts for a long time, until we got addicted to cordless. Then weight and power became more important than price, bringing fancier battery technologies into play.
So let's take a look at the batteries themselves followed by what the various companies are proposing, at least for the moment as technology is changing so fast, I may have to re-write this six months down the road.

Battery Types
NiCad - NiCad has been the standard tool battery since Black & Decker brought out the first one in 1961. It is relatively inexpensive, at least compared to alternatives. One major drawback is that it will loose its charge just sitting on a shelf, so you always need to charge up prior to a job. NiCad batteries fade at the end of a charge and loose power when hot, either from use or from sunlight. Modern smart chargers have eliminated the memory problems of NiCad batteries.

Nickel Metal Hydrate - More power for the same size and weight as NiCad, but more expensive and shorter life span. One unique drawback for Canada is poor performance in cold weather. The Japanese manufacturers embraced Nickel Metal Hydrate but before it gained serious popularity in Canada, the Lithium Ion battery came to maturity and is in the process of displacing this technology.

Lithium Ion - This is the technology that has always powered portable computers and cell phones - expensive little powerful batteries. Lithium Ion can put more power in a smaller package than NiCad and does not have the cold temperature problems of Nickel Metal Hydrate. In addition, there is no standby discharge and no fading at the end of the charge. It gives more power per charge and more charges for the life of the battery - some claim over 300% more battery than equivalent NiCad batteries. Beauty, but with a price.
It is important to note that as with most things, all Lithium Ion batteries are not equal. Lithium Ion is a category of technologies and the different manufacturers use different variants of that technology - as if it wasn't complicated enough to try and compare offerings already. For the same voltage with the same Lithium Ion label you can get different power storage (amp hours), different charging rates and different longevity of the battery itself. That is where the manufacturer's fine print comes into play.

Battery Specifications
Voltage - There is a direct relation between voltage and power in tools. 18v was for a long time the standard, considered the maximum practical weight with reasonable power, but not as powerful as a corded tool. Some 24v tools showed up claiming close to corded tool power, but they were heavy and did not take over the market. Lighter weight Lithium Ion batteries have permitted the explosion to Milwaukee's 28volt line - with claims to be as good as a corded tool - and then the DeWalt 36 volt line - with claims to be more powerful than a corded tool. Both of these batteries are close to the same weight as the old 18volt NiCad units, if not lighter. For those who are more concerned about weight than power, some manufacturers have already indicated that 18 volt Lithium Ion batteries will be on the shelves soon.

Amp hours (Ah) - This is kind of like the size of the gas tank - how long will the tool go on a charge. Amp Hours doesn't change the power, but it changes the amount of work you can get on a charge. A higher amp hour basically means you have more battery in the same size package. Some manufacturers are bragging about their battery's amp-hours while others don't even list this on their spec sheets, maybe because they don't have anything to brag about. Milwaukee's "fuel gauge" is an interesting extra, letting you know how much charge is left before climbing the ladder.

Cooling - Battery heat is a serious problem with powerful rapid charge and discharge batteries like those in power tools. Several years ago some companies started putting thermometers into the battery packs so that the smart chargers would refuse to charge until the battery cooled down or warmed up to room temperature. That helped to lengthen the life of batteries. As we get more and more power into smaller and smaller packages the batteries in the centre of the battery pack can age faster than the others because of heat. Bosch advanced the idea of inserting cooling rods between batteries to keep the centre of the battery pack from overheating, increasing the lifetime of their "Blue Core" battery pack by 50% they say.

Battery Chips - Temperature sensors are not the only things manufacturers are putting inside the battery packs. Milwaukee wanted to get a marketing edge on durability by giving a 2 year/1000 charge guarantee - free battery if it fails and another 3 years/1000 charges on a pro rata warrantee. To do that, they needed to know when the battery was first used and how many times it was charged - hence their Smart Battery chip that keeps track of your warranty information for you.

Dollars - It is interesting to see that weight, power and stored charge have become more important than price for many tool users. But not all manufacturers have put price last. Ryobi went in the opposite direction, marketing everything separately and bringing the 18v NiCad battery price down to $30. Remember, there are so many variables in batteries today that shopping by voltage and price alone will not tell you much about what you are buying, and there are times when a light duty tool is more suited to the job than a heavy duty one.

Chargers - If you are still using chargers from the first cordless tool you ever bought, it is time to update the chargers. Modern chargers analyze the battery and give it just what it needs - no overcharging, no undercharging, no hot charging and no cold charging. They make all batteries perform better and last longer. Some companies are beginning to bring out chargers that will charge more than one level of voltage, but only their own brands.

Backward compatible?
Will the new Lithium Ion battery work on that old NiCad drill? Milwaukee says yes; DeWalt says no; others say wait a few weeks. Bosch's new NiCad Blue Core does work on their old NiCad tools. Like it or not, since one company has done it and another is coming down the line, they will all eventually have to design in retrofit capability. But just like Beta video died and the movie studios have officially quit making VHS copies of films, someday you may have to throw out a perfectly good tool just because there are no more batteries for it.

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