Things To Do With Your Laptop Batteries When They’re Dead


[Roy] over at GeekDad had a dead laptop battery on his hands, and decided he would disassemble it to see what useful things he could do with the cells inside. He mentions in his article that even though your laptop might be convinced that its battery is toast, more often than not just one or two cells are damaged. This may not be news to all of our readers, but is worth pointing out to those who might not be aware.

With the bad cells separated from the good, [Roy] thought up a couple of different uses for his newly acquired batteries. His initial idea was to power an LED flashlight that was made to run on the 18650 cells he recovered from his laptop – not a stretch of the imagination, but definitely useful. The second use he came up with was to pair two of the cells together in order to simultaneously power an Arduino and some small Lego motors.

[Roy] lays out all of the standard caveats you would expect regarding the care and feeding of the lithium cells, and even suggests rebuilding the laptop battery as an option for the more skilled members of his audience.

Now we understand that dismantling and re-using old laptop cells is not necessarily groundbreaking, but it’s definitely something that’s worth a bit of discussion. [Roy] admits that his two ideas fall far short of the “18650 Things” his article title suggests, so how about adding a few of your own?

If you have stripped down some laptop batteries to salvage the cells, let us know what you did with them in the comments – we would be interested in hearing about it.

65 thoughts on “Things To Do With Your Laptop Batteries When They’re Dead

    1. Funny.I wonder what “mother Earth” would say when you finally go and join her.Would it be like “Sorry son,You already filled me with every junk you could have used again and there’s no space left for you”.Just sharing sme thoughts here…. cheers :)

  1. I got about 200 used ones from work, and tried to make a solar-rechargable pack out of them that would could power my 10 meter propagation beacon for days at time.

    The problems I ran into were three-fold:
    1) getting them to charge evenly (charging multiple cells of different manufacturing dates and conditions in parallel was very difficult).
    2) getting them to charge safely from the solar panel (I definitely wanted to avoid explosions).
    3) putting them together in some sort of mount that didn’t involve gobs of tab-welding of terminals (I slid the cells between a couple pieces of grooved angle-iron, and bolted the assembly together).

    Not insurmountable problems, but I finally decided to play it safe and use lead-acid batteries in my setup instead.

  2. Interesting, I hadn’t of thought to seek out chargers/uses for the individual cells. Do those battery holders have the protection circuit like the flashlight, or do you have to make sure manually to not drop below 2.7V?

  3. I have a box here of about 45 18650 cells from batteries.

    I use them in all my projects.

    I purchased an 18650 mains charger, and a bunch of other 18650 stuff like an ultra-bright LED flashlight.

    yes, my projects have UVLO for cell protection, set at 3V.

  4. the internal battery on my navigon 2100 gps went bad. so to save money i strapped a 18650 cell from a bad laptop battery pack to the back of the gps unit. then i reused the charging circuitry from the original battery. works really well, just takes alot longer to charge since it’s 2000mah vs. the 1300mah stock battery.

    1. Use a battery management circuit. They are cheap and can save your project from self destructing like that mega flashlight the other week.

      DealExtreme has single cell ones for a little over a buck a piece and other sites sell multi cell boards.

  5. i use my r/c heli charger to charge these kinda cells (and others, like cell phone batteries) through a number of makeshift adapters. i usually make 2 cell battery packs for arduino projects and powering wireless cameras, but i do sometimes make 3 cell packs since i can charge those too. those are good for light r/c projects. haven’t had any go boom yet.

  6. this makes me think of that tragic story of the guy who made the obscenely bright flashlight with loads of expensive LEDs and Lipo batteries that blew up and torched the whole thing. :(

    however, I also have a pile of laptop batteries that are still at OK voltages. and I don’t have expensive projects to put them in… how can i lose!? lol

    with proper care they’ll be fine. everything in life has a risk. as the user you must weigh that risk yourself.

    1. I installed an 18650 in a cordless phone and it could stay off the hook for over a month! It was not a protected cell and I stupidly only used hot glue to insulate the positive terminal after I soldered the positive lead wire on. It worked fine for 6 months. One day I tossed it on the work bench and it started smoking then shooting flames and spun like a pinwheel of death! When it cooled off I opened it and the majority of the surface mount components unsoldered themselves and fell loose from the housing! Thank God it didn’t blow when I had it upside my head! I would have ended up in a level 3 burn ward with a bed pan & morphine pump! Word to the wise,”Always make sure you use a protected cell in anything you hold up against your head!” lol

  7. I smashed one with a hammer enough times, it didn’t even vent.

    Another time I accidentally drove a small sharp object into one, and a large flame shot out like a butane lighter, and the whole battery was very hot for the next few hours.

  8. I make battery packs for my insanely bright homebrew LED bike lights out of old laptop 18650s, most recently a nice little 3P2S (7.4V, 6.6 Ah) number. I use a commercial “smart charger” and PCM (protection circuit module), as well as a polyswitch and lots of duct tape and waterproof wrapping to keep the pack safe. So far, no explosions while on the trails!

    Aside from the recycling, the nice thing about lifting cells from the same old battery is that the surviving ones are likely to be quite well balanced, addressing one of the many safety issues with Li-ions.

  9. I also found that there is often a nice piece of copper coated with iron phosphate foil inside some of the newer phosphate batteries.
    If you remove all the other chemicals off it, this can be used for all sorts of useful experiments.

    Haven’t tried this yet but supposedly you can make your own rechargeable batteries using two pieces of this foil.
    The electrolyte is a lithium salt which appears to be present in the separator.
    As long as it is then sealed up properly (heatshrink maybe?) then heat treated to reactivate the iron phosphate it should at least hold some charge.

  10. As in, two pieces of different foils, the carbon coated aluminium and the phosphate coated copper.

    Best bet is to cut two flat squares out of each foil with a piece sticking out on one side.
    Cut piece of separator to cover the copper completely then roll up the assembly and heatshrink.
    Seal the ends with superglue + baking soda or UV setting glue to prevent water getting in.

  11. I’ve been doing this for years, founbd out on my own that just 1-2 cells, or all of them, or the charging system is bad.

    We have recycling “buckets” at work for batteries, VERY nice resource for batteries. Dell is absolute junk, so I get about 20 of these a week if I remember to look.

    Big uses are one brand of e-cigarette vaping unit (cant think of the name), and my 1-watt blue laser from Wicked Lasers. Same battery. I use the Wicked Laser to charge them up, then run a load on them & see if the V drops significantly. If it does, back in the bin.

  12. I collected a set of 18650’s from “dead” laptop battery packs as a re-chargable, high energy alternative for the Nerf Stampede and Vulcan :)

    They’re also perfect for powering home-made colored LED lanterns for the kids.

    1. You’ve got to be kidding me! I was going to say the same thing, but only about the Vulcan. It’s a crew serve weapon mounted on a powerwheels vehicle and runs out of juice pretty quick on the stock supply of Ds.

  13. I bought a cheap camping lamp, packed it with 18650 cells and fitted an ultra bright LED, cost about £8 in total and lasts for days.
    I bought one of the cheap chargers from ebay, might get a few more and setup a charging bank.
    I’m hoping I can power an Arduino based clock with a bunch of these

  14. I have found they work great in packs for those cheap electric airsoft guns. With a charged set of them, they go all day damn-near.

    The only trick is charging them, but I’m lazy so I just current limit with a 1 ohm resistor and bench charge them. Piece of cake.

  15. Philpem built one a while back.

    I had a go too but as it turned out the expensive part is the capacitor bank.
    I tried to use a 1F audio capacitor but this didn’t work reliably for some reason.

    You do need a very powerful thyristor, the small low powered ones WILL NOT work, guaranteed.
    Although a possible workaround is to put FETs in parallel with small 0.1 ohm resistors inline to spread the current evenly.

    1. A generic 1F capacitor has way too much ESR to be useful. I have worked on a couple threaded stud welders that weld those little studs on to sheet metal. They use two of what looks like about 50,000uf caps and charge those up to about 200v DC. This is dumped to the work via a SCR. Weld power is controlled by a regulator circuit that limits how high the main caps are charged.

  16. I have 2 sets from 2 laptop batteries. Truly excellent!! Aside from using them as spares for my torch, my wireless doorbell receiver batteries (I was using 2 x NiMH) lasted less than a week and we would miss visitors, I soldered some flying leads to the contacts, ending in copper foil and used neodymium magnets to hold the foil in contact with the lithium cell. Although I have replaced a supply of ~3V with one of 3.7 it’s fine and the new arrangement lasts months. I’m planning to modify some other LED lights to run off them and build a simple, reliable, long-lasting rear LED light for my pushbike. The cheap ones keep failing.

    1. Indeed they could. You have to heat a large portion of the cell to get the end hot enough to solder to, which is where the potential fire hazard is; also soldering right to any rechargeable cylindrical cell is going to damage it’s vent, making it vent electrolyte more easily and shortening it’s lifespan too.

      They sell you cells if they weld tabs onto the ends though. Nickel tabs don’t take much heat at all to solder to, so not much if any makes it into the cell itself. They might also be willing to weld tabs to your cells if you bring them in.

  17. I took about 12 18650’s and made a replacement battery for an old Q beam. They fit perfectly and the light works better than it did before. Also, if two of these batteries are connected in series you can make a nice little rechargeable USB power source.

  18. I used two 18650 cells to make a “extended” battery for my Motorola Q9C smartphone. I believe the cells are 2200mAh. I fitted them to the phone by using one an original battery frame and circuit board (The original battery cell had become swollen), just soldered and hot glued to the cells, works fine. May make another one with even more cells just for insane battery life.

  19. Lots of talk about landfill, but lithium is actually safe (non toxic) once it’s oxidised. You can apparently neutralise a broken lithium cell by putting it in a container of brine (saturated salt water).

  20. Ah work in a computer shop, s’ Ah got boatloads a’ old laptop batteries on hand. Ah always pull the cells an’ use ’em. Ah light mah house with 18650’s an’ XML leds attached t’ old Athlon XP heatsinks. saves $$$ on electric bill, an’ makes good use a’ cells’d otherwise ned up in landfills. Ah got s’ many Ah don even buy primary cells anymore. Ifn Ah buy somethin that needs batteries, Ah pull it open an’ hack in a 18650, an’ a usb port fer chargin it.

  21. First, identify if only house numbered. !8650 batts are 18mm dia. by 65mm long! Whoda thought. Yes, parallel bat pairs from a laptop pack show up as excellently charge balanced. I always mark them with a letter as pairs before separating them. I cut off tab flush at negative end, leaving the long side on positive ends. It gets folded to 3-4 thicknesses to make the positive end titty. The common 2 cell chargers from China are parallel connected, so use them for balanced pairs ONLY. Else one cell will get hot and hog all the current, a runaway situation. For charging single cells, it is best to use a single cell charger. Yes, batt packs don’t have protected cells. To protect them from excessive discharge in flashlight service, replace the pair when you notice the light dimming. Protect batts from shorting! WalMart sells little orange waterproof containers of matches in the camping geat dept. They PERFECTLY fit single 18650 cells. The very best app for these cells is bright headlamps with 2 cells in a rear batt box. I’ll guarantee that using one regularly will improve the quality of your solder joints! In the long power outages which accompany winter storms here in the NW, I wear one which is continuously on when I’m awake. There is always bright light where you look. More than once after 2 days of use, I have gone looking everywhere for my headlight, only to find that it’s on my head working! It truly becomes part of you and you get so used to there always being great light wherever you look. I have Panasonic batts which are 18 years old still giving outstanding service. Once you try ’em, you’ll be hooked on them!

  22. I use a functioning laptop to charge batteries with a hacked battery case. I soldered wires to the hacked battery terminals. I then connect various single batteries to the wires to charge and discharge. I use the laptop running Hiren’s boot cd to monitor the batteries. I then use the batteries for various applications, such as for my bicycle lighting and such.


  23. same here …..i have recently started this project and surprisingly i just find just 2 or max 4 cells among 6 actually dead… others work fine ! i am planning to collect more of them to make a battery pack to power electric motors and thus the electric vehicles

  24. You must not allow the voltage to drop below design limits. Using an LED will help to stay within that range as LEDs will not work below their design threshold. Also do not charge them outside of their designed rate.


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