Why Rechargeable Batteries Are Rarely Cost Effective

I was standing in line at a local electronics store the other day when I struck up a conversation with the guy ahead of me who had a basket full of battery chargers and AA rechargeable batteries. It turns out he had decided to replace all of the batteries in his house with the rechargeable kind. Between the batteries and the chargers this guy plunked down over a hundred bucks!

He was so proud, telling me about all the money he was going to save.

I didn’t have the heart to ask him if he had the same typical electronic devices found in most homes, because if he did then he probably ended up spending a lot more money than he should have.

Rechargeable Batteries Aren’t Always Cost Effective!

I realize many people want to convert to rechargeable batteries for environmental reasons, which is fair enough. But the truth of the matter is this: when cost is the primary discriminator, low current-draw devices simply don’t warrant the extra expense of rechargeable batteries. That’s because the batteries of low current-draw devices are typically changed so infrequently that the payback period for equivalent rechargeable batteries would be too far long to justify the investment!

For example, it makes much more sense to use traditional alkaline batteries for low-draw devices like your wall clocks, radios, smoke detectors, programmable thermostats, and remote controls because they lose power at a much slower rate than rechargeable batteries.

And because traditional alkaline batteries can hold a charge for years when not in use, they are also the better choice for items that may sit unused for long period of time, like your alarm clock back-up battery and emergency flashlights.

When it comes right down to it, these low current-draw and/or low-use devices make up the great majority of battery-driven products in the typical home.

Okay.   So When Do Rechargeable Batteries Make Sense?

Rechargeable batteries are really intended for moderate to high current-draw devices that get at least moderate use. Typically, these are devices that require a battery change every 30 to 60 days.

In my house the only item that clearly met that criteria and, therefore, justified the added up-front costs of rechargeable batteries, was the kids’ Wii gaming system. That is a perfect example of a high-use device where rechargeable batteries will save you a lot of money in the long run.

But for my household those are the only items where rechargeable batteries make sense.

“But, Len, what about my wireless keyboards and mice? Those get a lot of use!”

Well, as my article on the practicality of wireless mice and keyboards noted, rechargeable batteries didn’t even make financial sense for those devices, based upon my battery usage over an 18-month period — I only spent a little over $18 on replacement batteries during that period. But a set of eight good rechargeable AA batteries (five for the mouse and keyboard plus three spares) would set me back roughly $24. Add in the cost of the charger (a good one can run upwards of $40) and you can see that the payback period on the rechargeable batteries becomes a real issue. Remember, rechargeable batteries eventually go bad too, so you’ll need your batteries and charger to last at least until the payback period is reached if you want to recoup your costs in a reasonable amount of time.

How Do I Know Which Type of Rechargeable Battery to Buy?

If and when you decide you want to buy rechargeable batteries, you’ll need to know that there are essentially four types to choose from: nickel metal-hydride (NiMH), nickel cadmium (NiCad), rechargeable alkaline, and lithium ion.

NiMH rechargeable batteries typically perform better than NiCads and are free of toxic heavy metals. Generally speaking, NiMH is the best all-around choice for most rechargeable battery applications. As an added bonus, most NiMH battery charger systems can accommodate NiCad batteries too (although the opposite is not true).

NiCads are being phased out in favor of NiMHs not only because they are losing the performance war, but also because of their inconvenience; the heavy metals used within the NiCad are toxic and require special disposal needs.

Rechargeable alkaline batteries have only two real advantages over NiMHs and NiCads: low cost and no need for special recycling. Otherwise, their long-term performance and recharge characteristics make these batteries a poor choice. Rechargeable alkaline batteries also require a special charger, which reminds me: don’t ever confuse rechargeable alkalines with the typical disposable alkaline batteries that are sold everywhere from 99-cent stores to the local grocery market – although some people do it, those batteries cannot be safely charged.

Lithium Ion batteries have great performance and can go unused for long periods without losing their charge. The big drawback is their price; not only are lithium ion batteries much more expensive than other types of rechargeable batteries, but they also require a special charger. Use them for rarely-used or high-drain devices like laptop computers, digital cameras, cell phones or portable televisions.

To help you decide which rechargeable battery is right for you, here is a trade summary I put together of the four basic options:

Click on the image to enlarge it.

 

Some Final Thoughts and Recommendations

  • A bad battery charger will prematurely age and greatly shorten the lifespan of your rechargeable batteries. Cheap chargers work too quickly, thereby heating the batteries, which damages them over time. Good chargers will keep your your batteries from getting too warm.
  • Batteries should always be removed from their chargers after recharging.
  • More expensive battery chargers extend the life of your rechargeable batteries by properly monitoring and controlling the charging process; many also shut off when charging is complete.
  • If you do use rechargeable batteries, be sure to keep several spare batteries ready to go at all times so you can swap them out when needed.
  • If you do choose to swap out all of your devices with rechargeable batteries, you can spread out your initial costs by replacing only the moderate-use devices first.   You can then buy rechargeable batteries for the low-draw devices as needed.
  • For info on NiMH rechargeable batteries and battery chargers, check out this article from MetaEfficient.

To Summarize…

Rechargeable batteries are great for moderate to high use devices that drain batteries quickly, but they are not cost effective for low current-draw and/or low-use devices – and it is the low current-draw devices that tend to make up the great majority of battery-driven products in the typical home.

Hopefully, the gentleman I met at the hardware store has a lot of high current-draw, frequent-use devices at his house — otherwise, he probably made a big mistake.

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Comments

  1. 1

    Dean says

    Nice article, Len.
    Why are there some devices that refuse to work with rechargeables at all? I have some kids’ electronic toys that won’t function at all unless they have disposable Alkalines. Some that come to mind are LED flashlights, blinky-noisy kids toys, etc. Maybe the cheap AAA rechargeables are to blame too. Can you recommend how to effectively compare price/performance on NiMH AA/AAA rechargeables?

    thanks, maybe topics for a future article…

    • 2

      Chuck S says

      Probably because NICd and NiMH are nominally 1.2 V and carbon-zinc and alkaline are 1.5 V.

  2. 3

    says

    Dean,

    I am going to put on my electrical engineering hat here to answer your question, but I will try not to get too geeky here… ;-)

    I’ll give a short answer to both your questions, followed by a more technical explanation.

    Short answer to question 1: The voltage drop on rechargeable batteries is often too high to get the needed peak power from the batteries.

    Technical answer to 1: Alkaline batteries have very high peak current ratings and good Watt-hr numbers (capacity). This is good for LED flashlights, which normally pulse the LEDs on and off at a high rate to get the brightness and avoid droop. Kids’ toys that have motors require high starting current and, therefore, alkaline are best for those applications too.

    Short answer to question 2: I think for home applications $/Amp-Hr rating is the way to go.

    Technical answer to 2: Normally, the battery industry compares batteries in this order of priority – energy density, cost per WHr, Amp-Hr ratings, pulse load capability (internal impedance), charge rate.

    Hope that helps! :-)

    • 4

      Matt says

      Not true about alkalines vs NiMH! NiHM batteries actually have a MUCH lower internal resistance than alkaline batteries. This means that NiMH batteries can supply a MUCH higher current than alkaline batteries. It also means that, although the open circuit voltage of alkaline batteries is higher than NiMH (1.5 vs 1.2), the voltage under a high current load is actually higher with NiMH batteries! In addition, NiMH batteries supply a more or less constant 1.2 volts as the battery is discharged, while the voltage of an alkaline battery drops with use.

      As far as rechargeables not working in some devices, this can only be the case in very low current devices. In these devices, a rechargeable battery may not produce sufficient voltage. However, in high drain devices, this will not be the case. Not only can rechargeables supply a higher voltage under a high current draw. But most devices designed for alkalines are actually designed to run on as little as 1.0 volts (since the voltage of alkalines tends to drop so sharply with use).

    • 5

      BC says

      What’s that about current and alkalines? You don’t seem to have taken internal resistance into account. Everything converts into a voltage divider. If the effective resistance of the device is high, like a wall clock – then the higher internal resistance of the battery isn’t an issue and nearly 100% of the voltage is available for the device. If the effective resistance of the device is low like with the peak operation of digital camera with flash, then there’s a severe voltage drop and a good portion of the power output of the battery goes into heating up the battery.

      The voltage drop on alkalines with high drain devices is severe. I used a multimeter on batteries in an old portable TV I owned. I could get about 3.5 hours out of either 3000 mAh alkalines or 1600 mAh Maxell (made by Sanyo) NiMH cells. When I measured the voltage, it was typically 1.61V for a fresh alkaline, but then maybe 1.1V measured when under load. For a freshly charged NiMH cell after settling down a few hours, I measured about 1.31V open circuit voltage, but about 1.2V when measured under load. After being drained, the alkalines would drop severely as the internal resistance increased. The NiMH cells still maintained decent voltage until they had a sudden voltage and internal resistance drop. In this portable TV, the alkalines would get extremely hot, but the NiMH batteries would barely get warm.

      The only issue is that some devices are only designed for the higher voltage of alkalines, and they don’t last very long until the voltage just craters.

  3. 6

    Richard says

    Hi Len,
    Nice job explaining the differences & economics
    .
    Re the Alkaline/rechargeable debate, alkaline (and the older carbon-zinc) batteries have a terminal voltage of about 1.5V unloaded when good. Rechargeable NiMH and NiCad are about the 1.2V area. Some electronics won’t start at the lower voltage.

    Also, NiCad batteries are regarded as superior to NiMH (and Lithium Ion IIRC) for low temperature applications.

    RP

  4. 7

    vicaya says

    Wow, there are still significant amount of people who don’t know LSD (low self discharge, which maintains 80% of the charge in a year) NiMH batteries. Google eneloop to learn more.

  5. 8

    says

    @Richard: Thanks. And you are correct about the NiCad and Lithium Ion for low temp applications. Lithium ion is especially effective in this regard.

    @vicaya: You are forgetting the cost equation. Alkaline AA batteries cost 30 to 40 cents each. It makes almost zero sense from a financial perspective to justify paying approximately $4 per AA LSD NiMH battery and another $20 minimum for a charger – those rechargeable batteries would go bad before you ever reached the payback period.

  6. 9

    Peter says

    Also, I guess, the main point you’re making about monetary cost would apply just as much to environmental cost? The numbers will be different (I don’t know quite how they stack up, & would be interested to hear!) but the basic argument – that if the batteries are only being replaced rarely, then the one-time cost of changing over outweighs the reduction in replacement costs – seems to be just as valid.

  7. 10

    says

    Good to know, but this article leaves out the convenience factor. It’s easier to have rechargeables on hand than to run to the store to replace the batteries for my mouse.

  8. 11

    says

    @Smarty: I think a lot of people would disagree with you. There really is no inconvenience at all if you buy the alkaline batteries in bulk, which you should be doing anyway. When I see the supply running low, I simply make sure I pick up more alkalines at my earliest opportunity. :-)

  9. 12

    Richard says

    Remotes have suckky range with rechargables in them because of the lower voltage.

    Also my cordless headphones will go louder with less distortion when run off alkalines. Shame the rechargable alkaline systems never got anywhere – I guess the 20 or so charges that you get out of them was not enough to swing most people to them.

  10. 13

    Jason says

    I actually just bought a Lacross BC-9009 Battery charger for $40 and 4 packs of Eneloop LSD batteries to replace my aging Energizer rechargeable setup. I think its a good investment for several reasons. First, everything seems to need batteries these days. 3 Wii remotes + 2 XBox remotes + 3 remotes for the entertainment center + Keyboard/mouse + Wii Fit Board + kids toys + other misc items. Second, is that to buy batteries in bulk, I would have to travel 25 miles to the nearest Wal-Mart — Highly inconvenient. Third, it is the environmentally right thing to do. Instead of landfills filling up with batteries, my batteries are charged by our town’s wind powered grid.

    Once you get over the hump of buying the charger, I think it makes more economical sense to get the rechargeables. At the end of the day, the rechargeables are going to outlast the disposable kind.

    • 14

      Darrell says

      Batteries are not supposed to go in the trash ever. Landfills should not get any batteries in them at all. They are supposed to be recycled.

  11. 15

    Erik says

    Provacative article, but I am not buying into your economic argument. Look at your keyboard/mouse example. $18/year disposable vs $24 for rechargeable (but You included 3 extra which is not a fair comparison – should be 5 at $15. Just after 1 year you are ahead on batteries) also the rechargeable last much longer than one year. My experience is easily 3 or more years. And if you are using rechargeables for all your battery needs the charger costs are spread over more batteries making the charger costs insignificant.

    Regarding convenience, it does make since to have some disposables on hand for when your rechargeables run down and you need battery power while your are charging.

    So, the guy in front of you was probably doing it right. Buying a lot of rechargeables which means he will spread the charger costs over more batteries.

  12. 16

    CTT says

    My MP3 player go through 1 AAA every two days and have done so for the last three years.
    Price comparison (local prices):
    4x LSD NiMH AAA’s: $8.50 + charger $12 = $20.50
    500x Alkaline AAA’s: $160

  13. 17

    Klaus says

    There also is another aspect to consider. Manufacturers still develop devices that do not make proper use of rechargeable batteries and that’s plain wrong. Devices should be designed in a way that they work perfect on rechargeables but can accept Alkaline batteries should you need to. The form factor of the rechargeables (and their Alkaline replacements) may not be perfect, but at least it is standardized. Not so for a whole range of devices (like mobile phones) where even within the product range of a single manufacturers you are faced with a multitude of proprietary rechargeable batteries which cannot be re-used/shared between devices AND device specific chargers. Totally ridiculous. That should be penalized IMHO. How environmental friendly is that? I also want to second another point someone brought up here: The more devices one uses that employ standardized rechargeable batteries, the less significant the charger costs become. We are a 5 head household with so many battery powered devices that I have two charges (one for 4x AA and one for 4x AAA types) running 24/7. Whenever one needs any they are swapped out.
    I opted for chargers that take their time charging because my understanding is this is more beneficial to the lifespan of the rechargeables due to the chemical energy storing process being less aggressive and more similar to the discharging pattern (so this might be a misconception of mine). Choosing the slow chargers, however, required some convincing of myself, because recharging cycles of 1hr only just sound very convenient. But when you need batteries, even a 1hr wait for charging is too long. Hence the setup of having two charges filled with rechargeabels all the time. I currently use NiMH. Why? Because I have a whole bunch of them. Once they die out on me, I’ll switch to the next best technology out there then — and probably buy two new suitable charges again.

  14. 18

    Andrew says

    Where did you get the ridiculous figures you’re using for the cost of NiMH batteries? I have a whole drawer full of the things and I never spent more than $1.50 on any of them (they’re all name brands — Duracell, Rayovac, and Kodak). The Wal-Mart by my house sells 4-packs for $5. The alkalines they sell run about 80 cents each when purchased in the large packages, or about $1 each when purchased in smaller quantity.

    I’ve used the same set of NiMH batteries in my wireless keyboard for about 3 or 4 years (8 or 10 charges) and they’ve paid for themselves in that time. I use NiMH in everything except the smoke detectors and I’ve only purchased one package of batteries in the last few years. I’ve got Logitec Harmony remotes which will burn through a set of 4 alkalines in less than 60 days.

    The total cost of all my batteries and the charger was around $50. It may have taken a while, but it has definitely paid for itself by now! As long as you get 3 or 4 uses out of each battery the cost is justified except for low drain+constant use items like a wall clock. Do people really leave batteries in things they only use occasionally when not in use? I know I don’t. Unless I use something every day, the only time it has batteries in it is when it’s in use.

  15. 19

    Matthew says

    I go through batteries like crazy and it just doesn’t make financial sense for me to buy alkaline.

    I’m having good luck with Tenergy Nimh AA & AAA batteries at well under $2 each. And you only have to buy the charger once. Sure, they might not work in a clock but I have exactly one clock that needs batteries. I have so many more devices that can use rechargeable batteries – cameras, tv remote controls, xbox and wii controllers, rc toys. Why on earth would I go buy batteries just to throw them away.

    Even in low draw applications these rechargeable batteries will still be working long after I throw away 4 sets of alkalines (equal cost wise).

  16. 21

    says

    I feel I need to correct one area you have commented on, and that’s the proper cell choice for LED flashlights.

    Contrary to your assertion in a previous post, most LED flashlights do not ‘pulse the LEDs’. They may employ PWM at lower intensity levels, but on high they must be considered high-current, high-drain devices. Many modern high-brightness LEDs demand more than 1 amp of current in flashlight applications, and will run at a significantly lower brightness if alkalines are used.

    Most flashlight hobbyists (and yes, there is such a thing) favor LSD NiMH cells for use in high power lights. They can deliver the high current required, have low self-discharge rates for storage purposes, and perform better at low temperatures than alkalines. NiMH cells also have a flatter discharge curve than alkaline cells, and can provide a form of regulated output in LED lights that do not use a regulation circuit. Additionally, NiMH cells have the benefit of not leaking over time and potentially ruining an expensive light.

  17. 22

    says

    @Richard: You are correct about the lower voltages of NiMH. This is also the reason why for devices that require more than 2 or 3 batteries, disposable alkalines (with their higher voltage) are often the best solution.

    @Jason: I don’t blame you for using rechargeables in your situation. Just make sure you buy the best charger you can, otherwise you will prematurely age your batteries. :-)

    @Erik: The main reason why I selected 8 batteries rather than 5 for the example is that the NiMH rechargeable batteries come in packs of 4 and 8. I do not know if you can even buy them individually and if you could the price would naturally be more expensive anyway.

    By the way, it is a fair comparison if the person buying the batteries (me) wants the convenience of always having fresh batteries available as replacements when the other batteries run down. ;-)

    @CTT: If I used my MP3 player enough, that would certainly be a good candidate. I’d be wary of the charger you have. That price seems to suggest you have a model that charges too quickly – if those batteries are warm to the touch when charging you really should find a better charger.

    @Andrew: My $24 price for rechargeable NiMH was based upon the cost for an 8-pak of 2700 mAH PowerEx batteries – arguably the best performing rechargeable NiMH on the market. I’ll wager your price is for the 2000 mAH Eneloop LSD NiMH. And that price is conservative, by the way, as they retail for $30. Of course, comparing the Eneloop to the PowerEx is comparing apples to oranges, but if you are interested I can send you some interesting test results that compared numerous NiMH batteries (mixed bag, LSDs and performance) and I agreed with their conclusion that the PowerEx was the better alternative. Then again, it all comes down to your applications.

    BTW, I can get a package of 36 AA Duracel alkaline batteries at Costco for 40 cents a battery.

    As for leaving batteries in things that aren’t used over long periods, I prefer to keep my emergency flashlight “loaded” at all times; who wants to look for batteries in a power outage?

    @Matthew: In your case, rechargeables seem more than reasonable. I just don’t think your case is typical. Yes, you will eventually get your money back using rechargeables batteries for low-current draw devices – assuming your batteries and/or charger don’t die before the payback period is reached. I have electronic clocks that require a new alkaline battery once every two years. At 40 cents per alkaline, the pay back period is over 6 years away – and that is not even considering the effects of the time value of money.

    @Michael: I don’t think Sanyo’s LSD Eneloop batteries are worth it for low-drain devices. From a financial perspective they are by no means any more cost effective than alkalines for the typical household. See my comment to Matthew for just one example.

    @Steve: Thanks for the correction – I know better than to argue with the flashlight enthusiasts! :-)

  18. 23

    lens42 says

    This article might be correct for old NiMH cells, but the conclusion is very wrong once cells like Sanyo Eneloop are considered. They self discharge only 15% per year, which means they are completely suitable for all but the lowest current applications. Since buying Eneloops, I have not purchased an alkaline AA cell in over a year. The only item still with alkaline is my TV remote. Flashlights, video-game controllers, digital cameras, and more are all on Eneloops and work great. I have never paid more than about $2 per cell.

    Eneloops don’t have have the 2700mA capacity of the cells used for comparison. They are only 2000mA/hrs but they are still superior because of the low self discharge. Before these cells, NiMH were unusable in most cases because after you charged them, and they sat for a while, you couldn’t be sure they were still full.

    The “low voltage” knock on NiMH is often not valid because NiMH (both Eneloop and older types) cells have lower resistance than alkaline, so even though the open circuit voltage is lower, the cell voltage doesn’t drop as much when it gets hit with a load. This is why NiMH have always worked better than alkaline AAs in digital cameras. Alkalines drop a LOT when the flash recharges, and trigger the “dead battery” indicator.

    I strongly implore readers to get a pack of Eneloops and a charger and stop filling the garbage with alkaline AAs. I am talking from direct personal experience. These cells work. Len is WAY off base.

  19. 24

    CanAmSteve says

    Great info, but as in the case of car ownership (not very cost-effective if public transport is available) once the decision has been made to purchase a good charger the equation changes, and that should be explored.

    I do a fair amount of photography and in flash units rechargeables (NiCads esp.) make more sense economically. Since I already have a sophisticated, multi-battery charger, my criteria for deciding what to use rechargeables in negates the cost of the charger.

    That being said, about the only other things I do use the rechargeables in is a wireless keyboard and some wireless speakers. I buy no-name AA and AAA alkalines in bulk (but have yet to find D cells). For low-temp use, lithium batteries work well but are not available in all sizes.

    I also tend to use alkalines in safety equipment like smoke detectors. As I replace the batteries before failure on a yearly cycle, I’m not sure how long NiMH cells would last, but the bother and possible risk are not worth it, IMHO.

  20. 25

    says

    @lens142: The conclusion of the article is that the batteries are rarely cost effective. Even if the NiMHs are LSD, the payback period is far too long to justify the expense of converting from cheaper alkalines. I stand by that assessment.

    @CanAm: Yes, if you ignore the cost of purchasing the charger then the equation changes, but why change the equation? The purchase price of the charger must be considered in the analysis. :-)

    Thanks to both of you for your comments. :-)

  21. 27

    Steve B says

    This article only works if you look at a payback of 18 months. My oldest rechargeables are approaching five years old and are used in everything from kids toys (low to moderate draw/use) to keyboards and mice to commuter bike lights (high draw, daily use). I don’t know if cycling them through a variety of applications matters, but in my case I haven’t bought a battery or charger in over three years.

  22. 29

    Ted says

    You have some good points. There are uses for alkalines and there are uses for rechargeables. I don’t think it is fair to only use the retail price of NiMH’s and then to use the “on sale” price of alkalines to make your cost comparison. Either use retail price of both or on sale price of both. Also, 18 months for the wireless mouse seems arbitrary. It seems like you would use it for 3 years (and even then might replace it with another one that also uses batteries) and for the second 18 months the rechargeables are free.

    I agree on buying a good charger, though you can get a good charger for $25 (on sale or at Amazon) that will 1. charge batteries individually instead of in pairs, 2. charge batteries at the non-damaging rate of 1-2 hours, 3. cut off when the battery is full. The $40 chargers are more versatile, but might be overkill. However, it is almost impossible to find good chargers in stores.

    Lastly, I think low self-discharge batteries can change things. They will be ready when you pick up the digital camera or flashlight after three months or a year since the last time you used it and you can take more pictures or shine the light longer than with alkalines. And they won’t corrode like alkalines that sit around for too long. If you get them on sale, you can stretch the 3-month cycle you talk about to 6-9 months and still be economical. LSD cells can be recharged thousands of times when using a good charger. And they will easily last 5 years or more.

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