Harvesting power-cells from dead laptop batteries for home electronics projects

Geekdad has a bunch of tips for using the round power-cells from a dead laptop battery. These cells, called "18650s," look like AA batteries, but have very different characteristics. Your laptop battery will contain lots of these (I have a mongo long-lived Thinkpad battery that I use while travelling with nine cells), and if any one of them dies, the whole laptop battery is rendered useless.

18650s are incredibly powerful and volatile, so be careful, because it's easy to blow 'em up or start a fire. That said, they're awful handy-dandy for providing a very long charge for very bright LED flashlights, or for powering your RC vehicles.

By the way, a good quality LED flashlight is incredibly bright. I tried to take some pictures and video to demonstrate just how bright, but you really have to see this with your own eyes, in person to appreciate it. And the LED is incredibly power-efficient, so it runs for a very, very long time on a single charge. It’s easy to see that the future of household lighting is not compact fluorescents, but LEDs...

In the video, I’m actually powering the Arduino as well as the motors, and I’m surprised it works. Motors tend to create a lot of electrical noise, and I’ve read about many other people who ran into trouble using a common power source for their Arduino and their motors. I presume I’d start seeing trouble if I was driving a heavier load than those little Lego motors.

18650 Things To Do With An Old Laptop Battery (via Red Ferret)


  1. I am getting very much annoyed with this “Maker”-crowd and their projects. This article, or its derivatives, does not contain ANY USEFUL FACT, just general adjectives. The “instructables” is the worst, it is totally impossible to comment or give sound advice, when 97.3% of the stuff is from total clueless pinheads, who hang around just to experience the wonderful feeling having somebody breathing and spitting into their face. Or something. Or whåtever.

    As regards to these 18650s. You can charge them with anything you want, if you regulate the voltage to 4.3 Volts and keep the current under 2 Amperes. I usually use cheap 7805s and a regular diodes to accomplish both. When discharging , you should not empty them much below 3 Volts, or they totally die.

  2. I agree with Christian.  Li-ion based batteries are wonderful things, but caution and a good understanding of what you are doing go a long way in not burning down your house or getting hurt.

    Also on a related note, a lot of the new cordless li-ion power tools use 18650 batteries (especially the 12V peak/10.8V stuff).  From what I’ve found replacement packs run from $40-$60 and that’s for a 1.5Ah pack.  You can get 2.6Ah cells for about $9 a cell.  So for about $30 and an hour of time you can rebuild your power tool packs, save some money, and get 70% more run time from them.

    Just to say it again, Li-ion and especially 3.7V cells (LiCoO2 and LiMnxNiyCozO2) can be very dangerous if you exceed things like charge rate, amount of charge, peak voltage, ect… 

  3. If the future of household lighting is really LEDs, is there any way to make them less ugly and harsh? They practically burn my retinas and actually give me migraines.

    1. I guess that depends on what you mean by harsh.

      There are good lenses for most led form factors and designs which can help give a more even dispersal of light.  All of the big LED manufactures make different grades and temperatures, which is probably a big source of the harshness.  LEDs with better color index are usually are more expensive, and ones with warmer tones (lower temperatures) usually produce less light.  For now I think you are going to see price to performance rule most of the straight replacement designs.  As sales go up and LEDs get better I think you’ll see more options and better quality show up.  In a way it is similar to the early CFLs.  You didn’t have many options and sometimes the quality/features were lacking.  Now you have everything from warm to daylight bulbs (2700k-6000k+), instant on, and flicker free.  In a lot of situations they really are better than regular bulbs.

      From the LED replacement units I have seen I’m not impressed.  I have an eye condition that allows me to see flicker up to around 100hz, and I’ve seen several that obviously are not filtered and flicker.  I certainly would not have those in my house.  I have heard of higher quality lighting units that use LEDs, but they are not cheap and not something you can go down to your local Lowes/HD and pickup.

  4. Charging/discharing 18650s can definitely be dangerous, especially if you don’t have a ‘smart’ charger.  You can however buy ‘protected’ 18650 cells from certain Hong Kong based websites for $2-$3 a pop.  The ‘protected’ bit of the battery is a built in circuit that monitors current flow.  If you try to overcharge it, the circuit will shut the flow to the battery off; if you try to drain it too quickly (or too low, rendering the battery useless) it will again disable the battery.  They last an extremely long time compared to any other NiMH or Alkaline battery available. 
    They are also 3V (Lithium based), so they will not be able to be used as direct replacement for AA batteries (1.5V).

  5. As soon as I saw this, I thought of all those exploding laptop videos on YouTube.
    This video just get’s more and more frightening:-http://www.youtube.com/watch?v=pizFsY0yjssI can’t really to add to that!

  6. I know this is really about 18650’s…and I agree they are great to play with if you are careful. But, my 2 cents on LED’s:  I’ve been messing with LED’s for 30+ years.  For what it’s worth, just know that LED’s are not yet nearly as power efficient as florescent tubes.  At higher outputs, you have to heat-sink them. That heat is wasted power.  LED’s are improving, but in general they are fairly narrow spectrum devices,  which is why they are perceived as harsh. This will improve with better phosphors and filters in time.  I do think LED’s will take over eventually, but there are *many* types of electric lighting technologies today that will be with us for a long time.  Perception of “light” and it’s various qualities is a deep and fascinating science. I encourage you to dig into it.

    1. every time i say to someone LED’s are not all that efficient at higher outputs they look at me if i just said the world was flat. I guess they have been brainwashed by the Green=good=LED=green movement. ALso: if you use heating in your house normal bulbs are way less wasteful than commonly portrayed. (and no plastic/mercury involved in the manufacturing either. If you using airco units than they ARE BAD ofc.

      1. ALso: if you use heating in your house normal bulbs are way less wasteful than commonly portrayed.

        …assuming you want a space heater instead of a lamp. 

        Edited to emphasize Swartzkip’s smartness and my stupidity.

  7. Brand-new, protected 18650 cells are so cheap from Chinese websites that it’s hardly worth harvesting them from laptop batteries, especially since the laptop battery cells are not protected and can be very hazardous.
    Also, 18650s don’t actually look like AAs – they’re a lot bigger, 14500s look exactly like AAs.

  8. I do this with the NiMH batteries from old radio battery packs.  They tend to use 7.2V packs, so six cells which are roughly AA-sized.  We scrap them at two years old, or 80% capacity.  They tend not to last long in heavy charge/discharge cycles because at two years old they’re pretty much done – consider that they will have been charged and discharged fully around 600-700 times!

    They’re free, though, since otherwise they just get hauled off for recycling.

  9. As a battery guy I have to say please don’t do this.

    A few things: When you modify an existing battery you remove all the agency approvals, this means that the “battery” you make out of the used cells is no longer approved for transport except as hazardous goods. If you take this on an airplane or even a vehicle without proper packaging and labeling and “something” happens you are now looking at large fines (few $1000 to tens of $1000’s per offense for improperly transporting hazardous materials depending on land sea or air).

    OK, so you’re going to experiment at home, fine, but if you crack the cell header, dent the cells, or generally abuse the cells, they can catch fire. Possibly at night when you’re asleep. Store in a fire proof area, discharge them fully (0V on cells) and recycle them once you’ve done your experiments. Don’t make flashlights for your friends.

    A lot of engineering goes into making battery packs safe. This stuff is really cool, and it’s neat to read data sheets and take apart batteries to learn how it all works, but it’s very subtle tech.

    1. Very helpful, thanks for your comments.  Do you have any links to more good info on batteries by any chance?

      Seems like taking the laptop batteries apart is an all-around loser unless you’re actually a professional battery refurbisher — others point out that safety versions of the cells are available for quite cheap online so there’s no real reason to incur the risks involved.

  10. LEDs may not be as efficient as CFL but there are plenty of places in the home where they are much more suitable. Small lights that remain on for long periods (night light, porch light, etc), the light in your fridge, landscape lighting. Also they should be the ONLY light used in a car other than the headlights. Turn signals that last decades, interior lighting that lasts as long as the car… it’s a no-brainer. I find it completely stupid that Acura in 2005, was still putting tiny incandescent bulbs in the controls on the steering wheel. Stupid stupid stupid. You have to unbolt and disconnect the airbag to get to these stupid lights that will burn out in less than 4 years and they will charge you $20 per bulb at the dealership. I took some LEDs and fitted them into the little plastic holders for the bulbs in the steering wheel and replaced them myself. Ford’s new Focus has all LED interior lighting. 

  11. my daughter and i regularly get lithium ion batteries w/ chargers for free on the local free-cycle mailing list from people who’s camera’s or phones have died.  our latest remote control boat will run quite a while on a bank of 4 tiny panasonic batteries.  building remote control cars and boats has really encouraged her to learn electronics at the age of 8.  she wants to build a remote controlled plane next, but i told her we would have to get a kit for that as aerodynamics is another can of worms altogether.  but building boats and cars from scratch is easy and fun.  i guess i’ll have to keep my eyes peeled for laptop batteries as well.  thanks for the info.

  12. Congrats on finally figuring out that CFLs are a stop-gap technology. Let me help you with a few other things – Bruce Willis’s character in “The Sixth Sense”? Dead. Luke Skywalker’s father? Darth Vader. Really.

  13. As a flashlight junkie my preferred cell is a protected 18650. I have eight unprotected 18650 cells from a laptop battery that had failed. There are real dangers with the use of unprotected 18650 cells. If you use more than one and they were not charged by a balancing charger or if you do not now how to manually balance charge the cells they will try to balance out when they are connected in your circuit. That means one or more of the cells is at risk of reversing polarity and exploding into a fiery death. If even a single cell is drained below a voltage that varies from cell to cell it will reverse polarity and burn. If one of these batteries has to much load put on it the cell can go into thermal runaway and once again burn and explode. This is the reason you won’t find these cells at regular retailers. If you do not know what you are doing with these cells they are dangerous. But, if you do know what your doing try substituting one of these for the 3X AAA battery pack in LED flash lights. They wont fit in the really small lights but any larger sized one should work. Makes that light VERY bright and it runs for a long time! BTW: candlepowerforums is an excellent source of info on this kind of stuff!

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