Salvaging Lithium Cells And Circuits

Lithium cells outperform Nickel Cadmium and Nickel Metal Hydride in almost every way. But they also need a little bit more babysitting to get the most out of them. That comes in the form of control circuitry that charges them correctly and won’t let them get below a certain voltage threshold during discharge. We enjoyed reading about [Carlos’] Lithium cell salvage efforts as it discusses these concerns.

He wanted to salvage a Lithium power source for his projects. He had the three cell pack from a dead Macbook Pro seen in the upper left, as well as the single blown cell from a digital picture frame shown on the right. The three-pack didn’t monitor each cell individually, so the death of one borked the entire battery. He desoldered them and probed their voltage level to find one that was still usable. To prevent his project from draining the source below the 2.7V mark he scavenged that circuit board from the digital picture frame. A bit of testing and the system is up and running in a different piece of hardware.

Don’t be afraid of this stuff. If you learn the basics it’ll be easy to use these powerful batteries in your projects. For more background check out this charging tutorial.

29 thoughts on “Salvaging Lithium Cells And Circuits

    1. Hi,

      I’m very interested in your experience. The PSP batteries were discontinued by Sony. I want to take the Li-ion pouch cell from a new cell phone battery (I’m not sure what but I would look at the Sony Ericsson models) and solder it again to the circuit board of the PSP battery and put everything back in the battery case. Do you expect this to be overly complicated or risky?

      Thank you.

      1. First: I’m not an expert!
        As long as the cells are fine (not expanding) and are off the same voltage and current rating then they should work.
        Second: If the cells have a different Ah rating then I have no idea how the charge cell will work.
        Third, there are several different charge boards with the battery contact in different places, what ever you do make sure you use the correct contact locations.
        forth Try brute fore powering the battery first without the circuit then add the circuit when the cell reaches voltage .
        What ever you do, let me know and I may add it to my post as a guest post.

        1. Hello,

          I found some time today to work on that project of replacing the Li-Ion cells of the PSP original battery. Pretty easy stuff, took pictures of the process, found the “donor” battery from where to take the cells… I’m doing testing now with a few discharge/charge cycles on the PSP. If everything works and you still need the description, I will put some words in a document and send it to you.


        2. Hello,

          I found some time today to work on that project of replacing the Li-Ion cells for a PSP battery. I found the perfect “donor” battery to supply the cells, I took pictures of the process… I now test the combination in a few charge/discharge cycles inside the PSP. If it works, I will gladly provide you with a material describing the work, if you still want it.


    1. No, don’t be afraid. I have salvaged at least a hundred cells and several tens of protection circuits, i have used these in lots of projects and i have never had a fire.

      As long as you make sure you don’t short the cells out, and that your soldering to the protection circuit is correct there is nothing to be afraid of.

      Have respect for lithium batteries, but don’t be afraid.

  1. You should most definitely be afraid of lithium based battery packs. They contain tons of energy, and unlike NiMH or NiCd, if you over-charge, under-voltage and then charge them, over-current them, puncture them, etc. they are very likely to explode. That doesn’t mean you shouldn’t hack with them, but you should treat them with the respect that they deserve.

    1. I think the statement ‘don’t be afraid’ indicates that it is dangerous but you should not be so afraid that you don’t ever do anything. And as stated you need to learn the basics first.

      And frankly I’m more concerned about people doing projects with radioactivity. It’s a silent invisible killer that does damage without indication.

  2. > Don’t be afraid of this stuff.
    *Do* be afraid of this stuff, it’s amongst the most dangerous things most electronics hobbyests deal with – but *don’t* not do it because it’s scary: just learn how to do it safely.

  3. The three-pack didn’t monitor each cell individually: WRONG! – Please have a look at the electronics in a LiPo pack- The circuitry inside a pack monitors the charge state (gas gauge) and monitors the individual cells to protect them from the most catastrophically problems. In the case of the dying MBP-packs with Sony-cells, one cell in the pack usually fails with too high internal discharge, dragging it’s partner down as well. There is NOTHING the electronics can do, since there are no balancing circuit built-in. The cells are being monitored, but nothing can fix the problem. Re-using these packs is a bad idea, unless you REALLY know what you are doing – AND have a LiPo/Li-Ion charging circuit. The electronics in the packs may protect the cells from over-charge and -discharge, but they do NOT protect from trickle-charging etc. that any battery-charger not built for Li-chemistry would perform. When trickle-charging Li-chemistry, metallic Li is formed between the anode and cathode inside the cell. ending in an internal short, and if you are unlucky, the cell turns into a hand-grenade………

  4. My late uncle used to do this all the time, he had an RC boat that could jump out of the water using old cell phone/laptop battery’s soldered together in packs. One day about 2 years ago out at grapevine lake the boat lost all response, the water was to cold so the boat is still out there somewhere. So if you are out at grapevine lake and you find this small RC boat full of old cell phone/laptop battery’s, please let me know.

  5. Take ‘er easy there Cap’n Snarkey. No need for toxicity in the comments, he’s not an idiot, he probably neglected to mention the danger because he assumed the readers are not idiots. If the content is so far below you, perhaps ya oughta move on… you know to awesomeland or whereever it is that people who have already attained all the knowledge available to to the human race ascend to. The rest of us is lernin, so we apreciate this stuff.

  6. Almost all laptop batteries only monitor individual cell voltages but don’t have a means of balancing. In the write-up the line “the three-pack didn’t monitor each cell individually, so the death of one borked the entire battery” wasn’t entirely true; the gas gauge detected that one cell was far off balance, and activated its safety mechanisms to prevent further charge and discharge. I’d also have bet that the gas gauge would have blown the on-board chemical fuse (in the case of laptop batteries, a fuse that can be electrically blown without the need for a high fault current) and also would have reported this in the Smart Battery System fault codes.

    Personally, there’s too much “lithium-ion-phobia” going around with using these batteries in projects. I don’t see anything wrong with reusing individual Li-Ion cells in projects, as long as you’re not an idiot when using them like trying to salvage over-discharged cells or trying to trickle-charge them. Proper charge ICs are easy to get (you can get ones that integrate all charge functions in one chip like the TP4056), along with battery protection (the OP addressed this with reusing a protection circuit, but these can also be bought from places like DealExtreme). If you want to have a “smart” battery pack, get a battery gas gauge chip (like TI’s bq27421) and interface it with a microcontroller. If you’re using an Arduino (or any MCU board really) you can use the chip to give you battery performance information.

    TL;DR – The laptop battery gas gauge did its job by preventing further discharge of the battery, and when it comes to reusing cells, it’s not hard to get the right chips to make sure you don’t blow something up. Don’t be an idiot with these batteries and you’ll be fine.

  7. Hi, I’ve reused MBP pouch sells before.
    Despite the dire safety warnings if the cells aren’t puffed and measure at least 3V when removed they are perfectly safe,
    I even saved a few controllers from phone charging units which contain the specialist
    algorithm needed.

    The only really important thing is if you do this, be aware that MBP cells have little sensors on them which cut the power if they are ever overcurrented/etc.
    I’d leave those well alone as they provide a vital safety buffer, and invest in the external PCB for each cell that cuts off power if the voltage dips below 2.7V as the charger ICs often leave it too late for that extra 10 minutes of runtime.

    As for puffed cells, if there is only a very slight puffing AND they have the external PCB then sometimes when slow charged at 3.85V and 100mA max they will de-puff and recover. If they don’t dispose of them safely and never try and deflate them.

    In case folks wonder, the fumes are a combination of carbon monoxide, HF gas and a few other “nasties” including ethylene.

    1. Before someone goes off on a rant here, that build uses a 2s2p config with high capacity, high current cells (he’s pulling 500W at 7.4V. That’s over 67A or over 12C load, that means he has to be using high discharge current cells, the most dangerous kind). He does mention increased self discharge in one cell. If that cell failed it would short out or load the other cell in parallel which is most likely what happened.

      So, when working with cells in parallel that were not factory matched and supplied in parallel, always use a protection circuit PER CELL (they are cheap, under a dollar each at DX). Especially if you’re working with high discharge current LiPo.

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