I first explored rechargeable nickel metal hydride (NiMH) batteries in earnest when I got my first digital camera. They've since taken over a shelf and drawer in my home office, and I recommend them highly both for the money saved and the recovered mental bandwidth (to understand what that means, read on).
- Hey, aren't these squirrelly batteries less powerful or something?
- So what are some of the good things about NiMH?
- Any negatives?
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- My Setup
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Hey, aren't these squirrelly batteries less powerful or something?
No, actually they're not. You may notice that NiMH batteries are marked 1.2 volts, and alkaline batteries are marked 1.5 volts. This is not a cause for concern, as NiMH batteries actually deliver higher average voltage over a use cycle than alkaline batteries. Rest assured, you can use NiMH batteries in nearly any device. Of hundreds of things I've used them for, the only thing I've noticed any negative performance difference with is my son's GeoTrax train set (the locomotives take 3 AAA batteries). They run a little faster on new alkaline batteries than on fresh NiMH batteries. Even so, the difference is quite slight and short-lived. As the alkalines lose their newness, they perform similarly to NiMH.
So what are some of the good things about NiMH?
Much lower cost. Yes, the initial cost is greater. A single high-quality NiMH AA cell can cost $2-3, while a single high-quality alkaline AA cell can cost less than $.50. But over the long term, the cost-benefit analysis greatly favors NiMH. Charge those NiMH batteries five or six times, and the initial cost is recovered. Charge them 60-70 times and you've paid for their charger. Charge them beyond that and you're putting money straight into your pocket.
Much better runtime than alkaline batteries in high-drain devices. Alkaline batteries perform very well in slow-drain applications, such as smoke detectors and remote controls. They do not tolerate high-drain applications, such as pocket televisions or radios, as well, and they do not tolerate extremely high-drain applications like digital cameras well at all. The NiMH chemistry excels at delivering huge chunks of power at once; the alkaline chemistry doesn't. A high-quality set of NiMH AA batteries can power a camera as much as 5 times longer than alkaline batteries. 50 shots vs. 250 shots is a slam-dunk no-brainer.
Longer runtime and more environmentally friendly than nickel cadmium batteries. Nickel cadmium (NiCad) rechargeable batteries have been around for decades, and they work fine. However, they don't have nearly as much capacity as NiMH batteries--usually only a fourth to a third of the capacity. Also, NiCad batteries are harmful to the environment and must be disposed of accordingly (at designated pick-up points and the like). NiMH batteries contain nothing harmful to the environment.
No memory effect. You can charge NiMH batteries in any state of charge without worrying about the cells developing a "memory." The worries about "memory effect" are overblown, even with NiCad batteries. But rest assured, it just doesn't happen with NiMH.
Recovered mental bandwidth. This is my favorite benefit, and one that I haven't seen nearly enough mention of. When you have a comprehensive NiMH setup (more on that below), you are essentially freed from thinking about batteries. There are always more batteries ready to go, you never have to think about where they are, and the only thing you're left to do is keep enough ahead of your new devices to ensure you always have some ready to go in "overstock." You'll probably find you can accomplish that with a couple of battery buys a year, which is a far cry from sticking batteries on the grocery list every few weeks and then wondering what you did with them when you need them. You can also stop worrying about what got left on in your child's room (or in your desk drawer, for that matter). Though it's good practice not to run NiMH cells down completely, high-quality batteries will likely survive it a time or two with no ill effects.
High self-discharge rate. Alkaline batteries lose power at a rate of a few percent a year. NiMH batteries can lose power at a rate of a few percent a week. This is not terribly inconvenient for most applications, particularly if you have a well-equipped charging station. However, it does essentially preclude their use in smoke detectors, burglar alarms, standby flashlights, and anything else for which battery failure could be a serious problem. Stick to alkaline (or better, disposable lithium) batteries for those applications. You might also keep using alkalines in slow-drain devices like preprogrammed TV and stereo remote controls, though for higher-end remotes with backlights and lots of features NiMH can make sense.
Some care required in handling. NiMH batteries are plenty durable for day to day use, but they are more sensitive to shock and impact than alkaline batteries. Severe impact, such as falling from workbench height onto a concrete floor, can destroy them instantly. Check such a battery out before using it again; if it has no power or its capacity is significantly reduced, it is ruined and should be immediately discarded. (I should note that I've never destroyed a battery this way in several years of heavy use, though the greatest impact I can remember subjecting one to was a fall from my desk onto a carpeted floor.)
High initial cost. It costs a bit of up-front money to put together a good NiMH setup, but as I said above, it pays for itself rapidly.
Use high-quality batteries. I have tried inexpensive NiMH batteries and found them wholly unsatisfactory, so stay away from the bulk brands like Powerizer. In my experience they are incorrectly sized (too large), have highly inflated stated capacities, and have an unacceptably large dud rate (10%+). Of major brands, I've also found Accu-Power and Lenmar to have inflated stated capacities and high dud rates. Moreover, Accu-Power cells are not at all tolerant of storage (individual cells can die permanently in just a few months). Avoid them.
I get excellent results from Powerex and Sanyo, and they're all I buy in AA and AAA cells anymore. They consistently test above their stated capacities, they hold a charge well, and they self-discharge slowly. Great products!
I've also gotten consistently good service from Gold Peak (GP) batteries. Stated capacities are accurate. In fact, I have some GP AA cells in service that are more than two years old and still testing slightly above stated capacity. The only thing that keeps me from rating them as high as Powerex is that the positive post on GP AA cells is just a smidge too short. It makes no difference in most applications, but I've run into trouble a handful of times trying to use GP cells in children's toys. For some reason, there is occasionally molded plastic around the positive terminal in a toy's battery compartment, with a cutout through which the positive post is intended to protrude and contact the terminal. GP cells come up a tiny fraction of an inch too short in these applications once in a while.
I have a few sets of Energizer NiMH cells, and am pleased with their performance. Energizer is usually what I get when I have immediate need and can't wait for a web order, as they're pretty widely available at Best Buy, Target, and the like.
Some brands I have some limited experience with include:
- Ansmann. Got some Ansmann AAs with a charger I bought. No complaints.
- CTA. I recently switched to CTA for C and D cells because there's enough difference in the price between them and Powerex cells to give them a shot. I have perhaps a dozen each C and D in service. No problems so far.
- iPower. Set or two of AAs here and there. They do what they're supposed to.
- Kodak. I've got a few Kodak AA cells bumping around, and they're just fine.
- Radio Shack. The first NiMH batteries I bought were Radio Shack. Performance is fine-I have some four-year-old AA cells still testing at 90+% of stated capacity-but be advised that Radio Shack NiMH batteries often cost more than twice as much as other choices of similar quality.
Use high-quality chargers. Good NiMH battery chargers charge batteries slowly enough to avoid excessive heat, and they switch to a trickle that keeps your batteries topped off after they have charged fully. In my experience, good NiMH batteries can be left on trickle charge for months with absolutely no ill effects. I've used several different Maha/Powerex chargers and have always been very pleased. I also have a couple of Ansmann chargers in service that have been good performers.
Mix different batteries in the same device. The batteries you install in a device should have identical chemistry and capacity, and should be in similar states of charge. Don't mix NiMH and NiCad (or alkaline or anything else). Don't mix 2000 mAh batteries and 2500 mAh batteries. Don't mix freshly charged batteries and ones that are nearly exhausted. When you do any of these things, the device can draw power from the batteries at significantly different rates because the stronger cells will continue trying to pull current through the weaker cells. At least, you risk destroying batteries; at most, you risk destroying your device.
Exhaust the batteries completely before recharging them. When you notice significantly reduced performance in your device, the NiMH batteries are exhausted and should be recharged. Do not attempt to run them completely empty. There is no benefit whatsoever in doing so, and it isn't at all good for the batteries, reducing their capacity and possibly even destroying them.
In my view, your level of satisfaction with NiMH batteries has a lot to do with how you approach their use. You can certainly realize benefit by keeping a couple of sets of 4 AAs for your digital camera--one set in the camera, the other in a trickle charger--and swapping as needed. However, if you want to use NiMH batteries in everything around your house for which it makes sense, go further. After all, different things take differing numbers of AAA, AA, C, D, and 9V batteries, so how do you keep all of it straight without mixing different battery capacities (which as mentioned above, is a no-no), swapping batteries in and out all the time, and the like?
The answer is to keep all of your common configurations on trickle charge all the time. That way you keep sets of identical cells together, and all you have to do is swap charged batteries for exhausted ones as needed. For example, if you have three devices that take 4 AA cells each and two devices that take 3 AA cells each, then you need a total of 25 AA cells: 12 for your devices requiring 4 AA, 6 for your devices requiring 3 AA, and 7 to keep on trickle charge (one set of 4 plus one set of 3). When one of your 4 AA devices needs batteries, swap them with your set of 4 on charge, and the exhausted ones charge for your next 4 AA device that needs batteries.
Why not keep only 4 in the charger? After all, that would enable you to swap with either a 3 AA device or a 4 AA device. There are two reasons this isn't a good idea. First, it's unlikely that all of your batteries will be identical, particularly if you embrace NiMH batteries long-term. You could buy some now, and when you need more they may not be available, or there may be better options. Remember that a device doesn't care whether it's running on 2000 mAh batteries or 2700 mAh batteries--the only difference is in how long the device will operate. So if you start with 25 2000 mAh batteries in the above setup, and then later decide to power another 4 AA device with NiMH, you could find that your 2000 mAh batteries are no longer available. No problem; buy what is available (2700 mAh batteries, in this example), keep them in sets, and you're good to go. Take your set of 4 2000 mAh batteries out of your charger and put them in your device, and then put your new 2700 mAh batteries in your charger, set to swap for the next 4 AA device that needs them.
Even if you plan to only use identical batteries all the time, the other reason this approach isn't the best idea is that you won't be putting your batteries in essentially similar conditions. With the above setup and charging only 4 batteries instead of the recommended 7, you could swap all 4 batteries for a 4 AA device. Then you'd only swap 3 of them for a 3 AA device. You can see that you'll quickly build different, constantly changing "sets" of batteries that have dissimilar histories. This will shorten their lives and can cause premature failure.
This is my charging station. On the left are five Maha/Powerex MH-C801D chargers.
The first MH-C801D has eight high-capacity AAs (Powerex 2700 mAh). This is what I run in my digital camera, my scanners, my shortwave radio, my GPS receiver, and the like.
The second has eight high-capacity AAAs (Sanyo 1000 mAh). This is what I run in my pocket TV, my blood pressure cuff, and the like.
The third has four regular-capacity (currently defined as <2700 mAh) AAs and four regular-capacity (currently defined as <1000 mAh) AAAs. This is what I run in everything else; this charger is for devices that take four batteries, obviously.
The fourth has two sets of three regular-capacity AAs and a set of two regular-capacity AAs. Another "everything else" charger, but this time for devices that take three and two batteries, respectively. (I find it useful to keep two sets of three on charge because so many of the kids' toys require three cells.)
The fifth and final MH-C801D: see the fourth charger description, but substitute AAA for AA.
The next charger to the right is an Ansmann Energy 16. You can find six CTA Ds (12,000 mAh) here. This is what I run in my toy robot. There is also a 9V living here.
The charger on the far right is an Ansmann Energy 8; identical to the 16 but with half the capacity. It's my dedicated C charger. Most of my C batteries are Powerex (3500 mAh), but I've just started stocking CTA (5500 mAh) as well, as they're much better value for the money. And one more 9V lives here.
The charger in front of the Ansmanns is a LaCrosse BC-900. I keep a single regular-capacity AA here, as the boys have accumulated a few items that take such lately. Mostly, however, I use it for diagnostics. It has an excellent capability set (mAh capacity, current voltage, and the like).
This is the battery drawer. Most of what you can see is alkaline storage, though you can see a few button cells in the back. Why so many alkalines? Well, as big a believer as I am in NiMH batteries, they're not the best answer for slow-drain or seldom-used applications, like a desktop thermometer, a remote control, a flashlight, and the like. So they're still handy. To the left of the tray are my "oddball" NiMH boxes. These are for orphaned cells (when I take three out of a new pack of four, for example). They live here until I can match them up with later orphans, replace worn cells in circulation, and the like. To the right of the tray is my current stock of new NiMH cells. I try to keep 8-12 each of AA and AAA in reserve, and turn them through the charging station once in a while. I also have a few Cs and a couple of 9V on the new side right now.
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