Reviving A Stubborn Laptop Battery

We’ve all gotten bored of certain toys and left them on the shelf for months on end. But what do you do when this prolonged period kills the batteries? Well if you’re [Andrew] you take apart the battery pack and bring it back to life!

[Andrew] picked up one of those Panasonic Toughbooks awhile back and although it’s hardly a top of the line laptop specs-wise, it does have some pretty cool features: it’s shock-proof, splash-proof, and extreme-temperature-proof. It even had a touch screen before touchscreens were cool. Despite its durability, however, the laptop was left to sit for a bit too long, and the battery pack no longer accepted a charge.

[Andrew] quickly disassembled the battery pack and began measuring the cells with his trusty multimeter, assuming just one cell had gone bad. Curiously though, no cells reported 0V. What he did find was that each cell and sub-pack reported 2.95V, which is 0.05V below the “safe operating limits” of typical lithium ion cells.

Figuring he had nothing to lose he tried his luck by giving the cells a direct boost with his bench-top power supply. He supplied the entire pack with a constant voltage of 12V for about 3 minutes while monitoring the current, and stopped charging once they each reached 3.2v. He then put it back together and the battery pack suddenly accepted a charge from the laptop once again!

We realize this won’t always work for a dead laptop battery, but hey, what do you have to lose?

42 thoughts on “Reviving A Stubborn Laptop Battery

    1. When a cell goes below 3V, you should charge it very slowly with a very small current. About C/10 or C/20 IIRC. So that would mean about 100mA. On the other hand, chances are you’ll hit the 3V and are allowed to charge faster after a few seconds…

    1. There’s a new way called EZbattery ( to bring nearly any type of old battery back to life so it’s just like new again. This method works with nearly every type of battery out there …and it’s simple and quick. In case you’re wondering, you’ll be able to bring car, phone, and laptop batteries back to life with this. It even works with solar/off-grid, marine, golf cart, and forklift batteries. Plus, many more!

  1. Has anyone had any luck with reviving HP batteries? I have tried this before but without any success, I think because HP has the annoying habit of making the batteries too smart, so when the voltage is too low, they shutdown forever via the firmware.

      1. I did just that, opened the package and charged the batteries manually. But the problem is that the board disconnects the batteries from the connector to the laptop and it reports the battery pack as 0%. It will no charge and it will not use the battery pack, while I know all the cells are ok. I’m afraid that HP does the same to battery packs as they do with ink-cartridges, “make ‘m too smart”, so that you have to buy new ones.

    1. that’s exactly why he closely monitored the current as it was charging, and stopped at the point that a normal battery would show as being “flat”. if the current is too high or the cell is punctured, or if it is overcharged, yes, it can burst into flames. as long as you aren’t an absolute idiot about what you’re doing and know the limits of lipo/li-ion you shouldn’t have any trouble at all

  2. I need to do this for my Nokia N900, someone had the bright idea of requiring the full OS to boot before it can charge a battery and there’s no hardware backup charging method. It can’t run from just USB power either. I’m unfortunately gonna have to buy a hobby lipo charger as I have 5v or 12 on hand but no 3.3 or anything safe to directly charge with.

    1. A 5V voltage source plus the right value resistor of the appropriate wattage in series to limit the current will safely charge the battery enough to be able to use the built in charger.

      I’ve had to do that many times with the battery for a Sony Ericsson X1 which had the nasty habit of inexplicably draining the battery. For ~50ma charge @ 5V, you’ll need a 39 ohm 1/4 resistor resistor. To charge faster, put a few of them in parallel. The tricky bit is holding the connection to the battery – bluetack or similar may do the trick. I strongly recommend putting a multuimeter in series to monitor the current.

    2. Or you can recharge that BL-5J battery in another Nokia, a lot of old phones used that battery some of them are cheaper than a charger. Here is a short list: Nokia 2010, 3020, 5228, 5230, 5235, 5236, 5238, 5800c, 5802, Asha 200, Asha 201, Asha 302, C3, C3-00, Lumia 520, N900, X6, X1, X1-00, X1-01

  3. If you use a bench supply with limited current and voltage, you should be safe. Just put the voltage value on the battery’s fully-charged voltage, and the charging process will stop once it is full.

    1. You are right that using a power supply with current/voltage limits is something that should’ve been done – his “bench supply”, however, looks like a converted PC supply; not something you can normally adjust the voltage/max-current with (not without mods or an external circuit).

      He was monitoring it, though (smart) – but what he did could’ve gone south quickly, and probably should’ve been performed outdoors, or at least with the battery/cells in a fireproof box, IMHO.

  4. I don’t get it. Battery management chips are suppose to go into trickle charge if the pack is that low. You should be able to pull the pack back to life with out this trick. But it will take many hours as, by safe design, the emergency trickle charge is very very slow.

    1. Panasonic toughbooks do this. he was just not patient enough to let it charge for 2 days.
      I have rebuilt 30 toughbooks from the CF-28 to current stuff and all of them have this feature. The problem is that the pack will probably have about 80,000 cycles on it and it’s not going to hold much of a charge anyways. You can get china knockoffs that work fine all over ebay for cheap.

      What is fun is using a chip clip to blow out the bios nvram/flash so you can reset the password, as many of these come with it set and the newer ones you can clear it by just removing the cmos battery.

    1. Right. LIPO batteries “get old” really really fast below the low-threshold. They do not start exploding when they have been “below threshold”, they just don’t provide normal capacity.
      That threshold is somewhere between 2.6 and 3.0V, but there is not much advantage of putting it lower, so many people/appliances put it at 3.0V. With the cells in this story living at 2.95, they are quite likely just fine.

      1. While you probably won’t get the battery pack back to original condition, you can at least get it working well enough that you can unplug the charger for a few minutes to change rooms. One of my old HP laptops had a battery that got a little too low and thus stopped working alltogether; a brown-out would make the thing turn off while a desktop with a decent PSU would stay running. This trick at least got me 10 minutes.

        1. To make that laptop survive a short brown out, if it has an external ac to dc adapter, add several capacitors between the leads right before before the laptop’s power jack. (separate the pair of wires, solder the caps on with the correct polarity and wrap with electrical tape) With a few millifarads added to your laptop’s power supply, it’ll keep it going a split second longer. Make sure the capacitors you use have a higher voltage rating than the adapter’s output, by about 50%.

    2. Sorry to say you’ve been fooled. If you’re paying a couple of dollars for a “new” 18650 cell, what you’re getting is actually recycled from a used battery pack, with a shiny new label on it. And the recyclers have no qualms with using cells that have suffered worse abuse than this. At least [Andrew] knows his cells have suffered minimally.

      To get Samsung 18650’s from a reputable seller where “new” actually means NEW, you’ll be paying around $8 per cell, or $72 to fully rebuild the pack.

  5. It’s a nice hack, if you don’t value your life very highly (or you have a great deal of safety equipment). I won’t be trying it, myself, even if it means wasting $100 on replacement battery packs — and I already have several fire extinguishers in every room.

  6. So, I have done this twice to my laptop battery (an HP 9-cell). I left my laptop pretty much discharged at the end of the Spring semester of school by accident, and then didn’t use it all summer. When I plugged it in and turned it on at the end of the summer, it informed me that it was “plugged in, not charging.”

    I was really disappointed because I had just purchased this new battery about a month before the end of the Spring semester, but I was able to revive it to what seems like full capacity by applying 12v, constant current to the pack via the output pins on the pack (no cracking the pack open, no siree.) I’ve had it happen once again, by accident, and was able to get it back working again without any problems or change in capacity, and have been running with this battery for about half a year; so far, so good!

  7. Could not leave a comment on his site as it is too restricted and not worth the bother of setting up so I’ll just post it here

    Seems these days that the charhers on these and other devices like cordless tool batteries are made to refuse to charge battery packs below a specified voltage . The above works on all of these .
    The battery packs however never really recover their zest and die again and again after not much more use.

  8. I discovered this method by accident. Plug in the charger, turn the device on for 2 minutes, turn it off and leave it plugged in for 5 minutes, then unplug the charger. Do this many times spread over many days. I discovered it with my shaver. After using the shaver in this way, once a day for a few months, the battery was revived. So I tried it with my old laptop. I used this routine for a couple months and the battery was revived. I don’t know how many times it actually takes, nor if they need to be done daily or could be done many times in one day. I had 2 successes and have not tried it again.

  9. Also useful to know: the actual lower limit for Li-CoO2 is a lot lower than this. I have found that if they are below 2.4V then they are generally hopeless BUT if you recharge them to 3.2V as mentioned it does work. Just don’t expect the capacity to be as good and there is a risk of Cu or Li dendrites forming. In fact low cell voltage can be a sign of anode damage especially on 18650s.

    Random note: 4.3Ah 18650’s are on their way!! Estimate 2Q 2019 when they get through UL/etc safety testing.
    Completely different construction and based on Mg-ion or so it is said, but otherwise very similar.

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