The Nickel Cadmium Battery
Ni-Cd... sounds familiar.
Good old Nickel Cadmium batteries... most of the younger generation were still in diapers when these batteries started being replaced by Nickel Metal Hydride and later, Lithium-Ion batteries, with which we're all too familiar. Those who remember Ni-Cd probably still have power tools or cordless phones kicking around in the house that ran off of these rechargeable batteries. And they probably still work! That's because Nickel Cadmium is awesome. It is by far the most impressive, yet still practical battery chemistry I have ever known. Sure there are lead-acid batteries that can draw hundreds of amps but they weigh a ton and die when discharged below 10V. There are feather-light and long-lasting lithium batteries but they explode and catch fire when you push them too far. We have the ever convenient and pervasive alkaline battery but they can't cope with high drain devices. Ni-Cd batteries have a special blend of qualities that make them solid performers in just about every category and they are versatile enough to be useful in almost any application. So why are these batteries so special and why can't you find them in stores anymore?
So what killed the Cad?
There are 2 main reasons for the demise of Nickel Cadmium batteries. The first is environmental. Nickel Cadmium, as the name suggests, contains Nickel and Cadmium metals, which are what the electrodes are made of. These metal electrodes, in combination with a gel-like electrolyte, produce the voltage at the battery's terminals. Nickel is a common metal found in abundance in the Earth's crust. Cadmium, a less abundant metal is particularly toxic to organic life and so any battery containing it has to be sufficiently sealed so as not to expose the cadmium inside. When these batteries are trashed at the end of their useful life, they often end up in landfills, instead of being recycled, as they should be. It's because of this environmental concern that other substitute battery chemistries easily displaced Nickel Cadmium. Nickel Metal Hydride had "similar" (yet still inferior) performance characteristics but without the toxic metal and its storage capacity was greater so it quickly became the battery of choice after its introduction. Later on, Lithium-Ion became the popular choice and so it remains today. It too poses no particular environmental hazard... unless you feel that the spontaneous ignition of your crotch is hazardous in some way.
I found it interesting to learn that another toxic battery chemistry, known as the mercury battery, which used to be used in high performance cameras, is no longer sold. Seems there's a pattern that all the environmentally unfriendly batteries are also the best performers but you can't find them anymore. Except for lead-acid. Those are toxic too and dangerous to handle but nothing else works well in a car so it escaped extinction due to industry demand. I guess even government environmentalists are somewhat... "practical".
The second reason Ni-Cd fell out of favor is driven by the technology itself. With new consumer electronics came new demands on batteries, foremost among them being longevity. Smart phones allowed people to talk for hours at a time while sporting a bright, full color LCD and computer-like applications demanding faster and more resource-hungry processors. In order to keep these devices going for a day or more on a single charge, a small, light and long-lasting battery was needed. Lithium-Ion batteries filled that space in a way that Ni-Cd couldn't, thus becoming the status quo in portable power for the 21st century. Since devices needed to last a long time but without taxing the battery too heavily, Lithium seemed the perfect solution. But as we will see, there are many other niches where Lithium and other modern day batteries simply can't compete with the old stand-by of yesterday.
Ni-Cd Batteries are BULLETPROOF!
The hard facts: Why Ni-Cd still kicks ass!
So what's so good about these batteries and why am I writing a hub about them? There are several good reasons:
- Nickel Cadmium is the cheapest battery available. While the up front cost is a bit high, these batteries can be recharged more times than any other battery before ultimately dying for good. When you factor in the number of charge-discharge cycles these batteries can survive, the $/cycle is actually lower than any alternative, making this battery the best bang for your buck!
- Ni-Cd is POWERFUL. All batteries can discharge at a certain maximum rate of current (measured in amps or milliamps) without being damaged. This is usually expressed as a multiple of their storage capacity in mAh (milli-ampere-hours). Therefore a 600mAh rated battery that can discharge 6A is said to have a rating of 10C where C is the capacity rating and 10 is the multiplier. Simply put, Nickel Cadmium has some of the largest C ratings of any battery (even more so than lead acid when you factor in weight and size). Gram for gram, Ni-Cd can release more electricity on demand without becoming damaged than anything else and this makes it ideal for devices that need a LOT of power but can't handle the weight of a car battery or the size of an equivalently rated Lithium battery.
- These batteries have one of the lowest internal resistance values of any battery. Internal resistance is how much electrical resistance is inside the battery itself, regardless of what you hook it up to. The higher the resistance, the lower the terminal voltage and the more heat you get. Have you ever tried to run a digital camera with flash and LCD screen using AA alkaline batteries? You might get 10-15 shots out of a brand new set of batteries before they are completely drained. This is because the camera drains so much current from them that the voltage drops due to the internal resistance and pretty soon, that 1.5V alkaline is only delivering 0.75V and the camera shuts off. Ni-Cd batteries on the other hand will sit at a steady 1.2V and keep grinning the whole time while you take dozens of photos.
- Nickel Cadmium batteries are durable. You cannot kill these things. You can use them in the freezing cold, in the stifling heat, you can drop them and bang them around. You can overcharge them, undercharge them, reverse the polarity (to a degree) and leave them derelict on a shelf for 15 years. You can even bring them back to life when they are shorted by "zapping" them with a high current pulse. Try abusing any other battery like that and see how long it lasts! All the popular batteries used today have major Achilles heels that will kill them easily and sometimes all it takes is discharging it a couple of volts below it's operating voltage or pricking the battery with a pin (don't ever do that with Lithium or you'll set the house on fire).
- As mentioned above, they don't die from being neglected. Ni-Cd is one of the few battery chemistries that actually prefers to be discharged. It therefore has no special maintenance requirements and you don't need to keep the voltage topped off. This is a huge perk when you don't need a device for long periods of time and then suddenly you do need it! For phones this may not matter because you use your phone every day but what about your drill? I wouldn't want to spend $100 on a new Lithium drill battery every time I don't use it for a couple of years.
- Ni-Cd has a very stable working voltage of 1.2V. Most other batteries have a terminal voltage that gradually decreases with remaining capacity but this reduces their "useful" life as they are unable to power the device, even though there is still capacity left, as is the case with AA alkaline batteries in a digital camera. Furthermore, because of this voltage drift that alkaline batteries are susceptible to, most devices that require them are designed to operate on a rather large range of voltages. Ni-Cd with its 1.2V is only 0.3V less than that of an alkaline battery, so it will always work as a direct replacement and often work better!
- Ni-Cd batteries can charge faster than any other battery type on average. While most batteries become damaged if charged at a rate higher than 1-2C, Ni-Cd can cope quite well with 4C or greater, allowing for rapid charging in a matter of 10-15 minutes. You might think this is a fallacy because car alternators can dump 100 amps into a car battery without damaging it BUT car batteries have large capacities on the order of 60-80 Ah usually. Therefore 100A is in the neighbourhood of 1.5C. Some performance lithium polymer batteries can handle up to 5C charging but they are specially designed for this purpose. Ni-Cd chemistry doesn't need any special treatment. Dump all the current into it you want (within reason) and it will handle it just fine. Very convenient when you finish racing your RC plane and want to get another run in without cooling your heels for an hour.
- One notable piece of trivia is that Ni-Cd batteries have no special shipping and handling restrictions. Lithium batteries on the other hand are considered hazardous and many of them get stopped at the border during transit. Aircraft won't let you carry them either because of the risk of combustion.
Look at that performance...solid as a rock!
And... where would you use these Ni-Cd wonders?
There are a lot of niches for Ni-Cd technology that will never become obsolete so there will always be a need for these batteries to fill:
- Power Tools: I cannot stress enough how perfect of a fit Ni-Cd is for this application. Power tools draw several amps and sometimes brief pulses in the 10s of amps. Even a small 600 mAh cell could operate at 30C for brief periods without breaking a sweat and that's precisely what power tools require - irregular sustained and burst currents on demand. Plus power tools are used in abusive, inhospitable environments where Ni-Cd batteries will reliably work and put other batteries to shame.
- RC Hobbies: Model planes and cars are really cool and there is a huge following for building and competing custom models. Ni-Cd batteries have always been and continue to be a popular choice for model planes, cars, boats and other motorized vehicles because they strike an excellent balance between size, weight, power and durability.
- Cordless Phones and Walkie Talkies: Wireless technologies tend to be resource hogs, especially when it comes to 2-way communications. Unlike cell phones, which merely need to transmit far enough to reach a cell tower 1/2 a mile away, walkie talkies need to transmit directly to another handset several times further than that, so they need to operate a much higher power levels. Ni-Cd batteries provide reliable, long-lasting, power and can be easily and quickly recharged.
- Emergency Standby Equipment: Things like portable radios and flashlights benefit greatly from Ni-Cd batteries because you can trickle charge them for years and when you finally need them, you have power on tap without a second thought.
- Digital Cameras: Another high drain device, digital cameras are battery killers because they cause so much power to be dissipated internally within a battery that there's nothing left at the terminals to keep the camera working. Since Nickel Cadmium has a very low internal resistance, almost all of its capacity is available to the camera and the chemical reactions inside can easily keep pace with the power demands.
- In industry: Ni-Cd is commonly used in portable medical equipment, in universal power supplies and in satellites, where its "heavy duty" rating is valued above all else. These devices have to work at a moment's notice and cannot afford to fail. Other more delicate battery types need to be babied and maintained so they don't become damaged or lose too much capacity.
DJ Bob jumpin his car with a Ni-Cd drill battery
How can I use these and where can I get them?
Nickel Cadmium batteries come in all the familiar sizes like AA, C and 9V but are also available in some exotic sizes better suited for constructing battery packs. This probably evolved from the common need to create custom packs for high drain devices that weren't heavily driven by the high-end consumer market but rather the industrial sector. You'll find that some of these less common sizes are rather convenient for your project and can easily fit into a wide variety of packaging spaces and cell configurations. In any case, you can find a wide variety of sizes and can purchase them either as individual cells, as cells with solder tabs (so you can easily make your own packs) or as pre-made packs of different voltages.
As for where to get them, if you can find a dedicated battery store, they may carry some Ni-Cd but your best bet is online distributors such as Mouser, Digikey and especially hobby shops because they stock these batteries for hobby builders. Ebay and Amazon are also worth checking out. I recently found a surplus of brand new Cadnica KR-600AE batteries on Ebay, which are one of my favorites... very versatile cells. There are still plenty left as of this writing so do a search on Ebay and you'll find them. The market share is small these days for Ni-Cd but getting your hands on them is truly rewarding. Buy 8 AA size and I guarantee you'll never need to purchase AA alkaline batteries in the next decade. Meanwhile I've chewed through 24 packs of alkalines in 6 months!
She's old but she'll hold
I've got Cads sitting on my shelf from my university days a decade ago that I still use today as if they were new. A lot of people take batteries for granted. Apple doesn't even design their phones with a battery socket because they expect you to either break your phone or buy the next one before the battery has any hope of dying but that only obfuscates how fragile these things actually are. When it comes to power-hungry work horse devices, there aren't many options that will do that job well, no matter how neglectful you are or how long you keep your device. This author believes that Ni-Cd batteries therefore will always have a unique purpose in portable electronics that is hard if not impossible to fully replace.