Ni-Cd (Nickel-Cadmium) batteries have been around for a long time. Forever, it seems. And they have served an incredibly useful purpose. After all, we wouldn't have cordless tools were it not for the invention of Ni-Cd rechargeable battery technology. But now I feel that the time of Ni-Cd has come to an end. A bitter, well-deserved, highly violent end. Why? Because I am an impatient tool user. Because I have seen the future and embraced it. Because I am sick of replacing my batteries every one to two years whether I want to or not. And most of all, because I am tired of picking up a cordless drill and having the battery be dead when I really need to use it.

Let's face it. In terms of what's available today, Ni-Cd sucks.

Tech Note on Ni-Cd: The nickel-cadmium battery is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes. There are two types of Ni-Cd batteries: sealed and vented. All Ni-Cd power tools use sealed cells.

With the current NiMH, and especially Li-Ion battery technology - well, Ni-Cd just doesn't cut it anymore. Back in the 80's and 90's when Ni-Cd dominated the scene, it was a breath of fresh air. Ni-Cd has several distinct advantages over lead-acid technology and alkaline equivalents. Rechargeable technology favored the Ni-Cd solution and soon every portable device had some kind of integrated Ni-Cd battery (even if it was only available through a third party supplier).

Fast forward to the early 1990's. A new sheriff entered the town called NiMH. Now we had the promise of greater power for less space, cheaper manufacturing costs and tools that ran longer on a charge. Of course, what they didn't tell us is that NiMH batteries discharged, on average, 5-10% the first day and then 0.5-1% every day thereafter (compared to Ni-Cd's 10% per month discharge rates). This meant that NiMH wasn't going to help us with low-power electronics like remote controls, clocks, or portable devices, but it was an excellent choice for high-power applications like cordless drills/drivers. Eventually, they figured out the discharge issue (around 1995, actually) and NiMH started really taking off (discharge rates dropped to 20-25% over a year).

Tech Note on NiMH: A nickel-metal hydride cell, abbreviated NiMH, is a type of secondary electrochemical cell and uses a hydrogen-absorbing alloy for the negative electrode instead of cadmium. As in NiCd cells, the positive electrode is nickel oxyhydroxide (NiOOH). A NiMH cell can have two to three times the capacity of an equivalent size NiCd. NiMH is typically fashioned into batteries for applications where a higher voltage is needed, such as in hybrid cars, radio control vehicles, cordless phones, and even spacecraft.

But wait, what's that? Lithium ion? A new battery design that has one of the best energy-to-weight ratios, no memory effect, and a slow loss of charge when not in use. In addition to uses for consumer electronics, lithium-ion batteries are growing in popularity for defense, automotive, and aerospace applications due to their high energy density.

Of course if you overheat or overcharge them they can explode.

Haha, just kidding... No, no I'm not. But still, this is rare (unless your name is Sony) and for the most part we haven't heard of any tools exploding - just laptop computers. To keep the batteries properly regulated, li-ion batteries usually contain a small circuit that shuts down the battery when discharged below a certain threshold (typically 3V) or when charged above a certain limit (typically 4.2V). It's simply the price we pay for better performance.

Tech Note on Li-ion: Lithium-ion batteries (sometimes abbreviated Li-ion batteries) are a type of rechargeable battery in which a lithium ion moves between the anode and cathode. The lithium ion moves from the anode to the cathode during discharge and from the cathode to the anode when charging.

A couple tips on li-ion batteries:

• Li-ion batteries, unlike NiMH or Ni-Cd, should be charged frequently - and before they "need" to be. If the battery is not to be used for a long time, it should be charged roughly half way.
  
• Li-ion batteries should not be fully discharged and recharged frequently (this is referred to as "deep-cycling"). Remember this, because it goes against everything you know about Ni-Cd.
• Li-ion batteries should never be fully depleted (to below their minimum voltage).
• Heat kills li-ion batteries faster. Believe it or not, keeping them in the refrigerator is actually good for them (though we don't recommend it - just keep them out of direct sunlight when possible).
  
• Don't buy 10 li-ion batteries if you only need 5. Li-ion batteries have a finite lifespan - and the aging process begins as soon as the battery is manufactured. On average, they lose about 4-20% of their capacity per year, though the charge time reduces as well. If stored at ~50% capacity and if kept at room temperature, the capacity loss of li-ion will stay towards the low end of the spectrum.

I like lithium ion technology for a number of reasons, the least of which is that charging time is cut by roughly 75% in most cases. Memory effect is gone, though battery life will shorten regularly over time. Still, this beats an unpredictable "battery death" which is the case with Ni-Cd technology.

DeWalt (and some other manufacturers) use a newer lithium iron phosphate cell based on research licensed from MIT. While the battery has slightly lower energy density that other competing Lithium Ion technologies, a 2 Ahr cell can provide a peak of 70 Amps without damage and operate at temperatures above 60 degrees C.

Lithium polymer batteries are hitting the market in droves, but are still mostly limited to portable electronic devices. The advantages of Li-poly over the lithium-ion design include lower cost manufacturing and being more robust to physical damage. They are also slightly lighter since they don't require a metal battery casing. They are have around 20% higher energy density, meaning you get 20% more power for the same volume. More power, less weight.

We haven't seen any official announcement or display of lithium polymer technology in power tools just yet, but our guess is that it's coming and will possibly start with smaller tools and work its way up to full-sized ~12-24V models.

So where does this leave us? Boycotting Ni-Cd, that's where. In our view there is no reason to ever buy a power tool that still runs on Ni-Cd... Except one. Yes, there is one very good reason to buy a Ni-Cd powered tool. Let's say, for example, that DeWalt is blowing out one of their older Ni-Cd drills for half its MSRP (maybe they are readying a new model or some retailer is having a close-out sale).

Buy it. 

Why? Because some manufacturers, like DeWalt, have made their tools "forwards compatible" with the newer batteries. After all, the tool doesn't care how it gets 18V - just so long as it gets those volts and there is an adequate recharger for the battery. So Ni-Cd still has a purpose afterall. In fact, this story comes about after one of our staff writers found some deals on some DeWalt tools. While he was bummed it wasn't Li-Ion, it was simply too good to pass up. And when he upgrades to the new Li-Ion batteries - the tools will still work perfectly.

Of course some manufacturers don't play as nice and will force you into a new form factor. This is because they completely redesigned the weight and layout of their tools to work with the lighter Li-Ion batteries. Here is a quick "cheat-sheet" on what's going on in the marketplace right now:

From the above chart you can see there are a few good reasons to still purchase Ni-Cd tools. Their names are DeWalt, Hitachi, Milwaukee, Ridgid and Ryobi. I haven't had too many drills give up the ghost on me, but plenty of batteries have gone the way of the dodo (let's see how many euphemisms for "death" we can come up with in one sentence). With that said, be a bargain hunter - and shop around for tools that you will someday use with lithium ion fuel instead of the "I'm going to die on you when you need me the most" Ni-Cds.