Save An Old Drill From Landfill, With Some Lithium-Ion Magic

What do you do, when your trusty cordless drill starts to lose battery capacity? You bought it a decade ago and parts are a distant memory, so there’s no chance of buying a new pack. If you are [Danilo Larizza], you strip away the old NiMh cells, and replace them with a custom pack (Italian, Google Translate link) made from 18650 Li-ion cells.

The build is a straightforward one to anyone familiar with lithium-ion packs, but to a battery newbie it should serve as a handy step-by-step description. He starts by selecting a range of matched cells from discarded laptop batteries and adds an off-the-shelf battery management board to keep everything safe. Interestingly he appears to have soldered his wires to the cells rather than the more usual spot-welding, sadly for many of us a spot-welder is beyond our means. It would be interesting to know both the mechanical integrity of the resulting connection and whether the heat of soldering might in some way affect the cells.

Firing up the drill with the new pack is not the immediate success he hoped it would be, the start-up current is so high that the battery management board goes into a fault condition. This situation is resolved with a model that can take more current, and he can take his drill out once more.

If you are annoyed by the rise of cordless tools, you’re in good company. Meanwhile if you lack a spot-welder for batteries, have a look at one of the nicer ones we’ve seen.

39 thoughts on “Save An Old Drill From Landfill, With Some Lithium-Ion Magic

  1. I had an old 24 volt sealed lead acid Weed Eater string trimmer (also sold under various other brand names). It was given to me with dead batteries so I bought a new pair.

    It worked well for about 3 years but last summer it was getting sluggish. With the trigger pulled the voltage across both batteries dropped to 5 volts.

    I’d looked into a lithium ion upgrade but it was cost prohibitive three years ago and the same in 2018. Cheaper to just buy a new Ryobi ONE+ trimmer with a larger cutting swath and also get a second dual chemistry charger and higher power, cold tolerant battery that works with the saw and other old blue Ryobi tools I have.

    1. if you run your ryobi packs down and the charger won’t charge them, take the lid off the battery and put +12 to the tabs for a few seconds, then slap it in the ryobi charger.

      I picked up the ryobi one+ trimmer at a yard sale with two batteries for $10, between pawn shops and junk stores i’ve got like 8 batteries, two chargers, three drills and a 1/4 impact. my only new purchase of the series was the 1/2″ impact and hammer drill.

      its not contractor grade stuff, but its cheap and available. works great for my needs.

  2. I’ve been repowering my NiCd (yes) tools with NiMH cells for years. The chargers are effectively interchangeable and the results are very good, so having to rebuild the entire chain (charger etc.) seems like a lot of unnecessary re-engineering once you’ve gotten past the proof of concept fun. The website claims “a costo Zero” but the charger changeover etc. isn’t free even if you’ve got salvaged cells to play with.

    That said, you can indeed solder to cells directly – I’ve soldered directly to dry cells back in the day when battery cases weren’t readily available (or I didn’t have the money for them), NiCd, NiMH, Li-Ion, coin cells (2032 – I don’t think the tiny ones would do very well) etc. The trick is to use a fine-tipped iron, flux and to keep the idea that you don’t want to heat up the whole cell, just a tiny part of it. Get a small bead of solder to stick, let the cell cool, expand that bead to a contact area, let it cool if necessary, then lay in the tinned lead. Slow but finally a very good connection. In more than five decades I’ve never ruined one.

    1. NiCd chargers usually use just 1/10C current charging, and sometimes have 12h timers, sometimes they don’t. NiMH chargers use minus delta V charging (good/fast ones) or 1/10C charging with timer termination (slow/cheap ones). So technically you can have problem if you keep charging NiMH after it’s full but in practice NiCd charger will usually have small charging current and not enough voltage to seriously damage NiMH.

      1. Most high quality NiMH cells are rated for continuous overcharge at 0.1C — I did the research for a product I worked on. Check the mfr datasheet to find out whether yours is.

        In general, NiMH cells are drop in replacements for NiCd. Which prompts the question: why are manufacturers still selling NiCd replacement packs for old tools, when they could be upgrading them to NiMH? Bonus: NiMH don’t have the annoying “feature” of cells shorting out when left unused that HiCd has. It’s not “memory”, it’s whisker growth that shorts the cells. NiMH seems to be more immune to this (though not totally).

        1. Exactly this – the trickle-charger versions are no problem at all, though I did replace my Makita charger for a used one rated for NiMH. Also NiMH cells don’t self-discharge nearly as badly over time – they’ll hold a charge for months and months, and don’t seem to be bothered by cold weather nearly as much.

          1. Yes, it is possible to use high current pulses to blow out the nickel whiskers. But they (or others) do tend to grow right back. It’s an annoying “feature” that makes NiCd battery packs less than ideal for low duty cycle intermittent use. You get about 4 years out of them before a cell shorts. NiMH seems to do better, in my experiece, it’s less about cells shorting than cells which won’t take a full charge.

            Experience: portable ham radio transceivers and battery powered tools. EE designing with batteries: NiMH and Li* (LiIon/LiPo/LiFe) pimarily.

        2. NiCDs have better cold weather performance in power tools, and they’re more robust against reverse charging which can happen when the pack is nearly depleted and some of the cells flip their potential (i.e when you just have to get that last screw in).

    2. Spot welding is the only safe way to attach leads to rechargeable batteries. By the time you get the battery case hot enough to melt solder, there’s a good chance you will have thermally damaged the innards.

      A cheap Chinese spot welder (yes, they can do some things right) is about $150:

      or, you can make one yourself out of an old microwave oven transformer:

  3. I’ve been meaning to fab up a adaptor so old Makita power tools (those with iconic red battery packs” can use modern li-ion packs.
    Problem is how to effectively and precisely limit current (without any slow drain when tool isn’t in use) in case of motor stall as those old Makita power tools don’t have any fancy protection electronics but relied on the somewhat low current (compared to lithium batteries) nature of the funky 2/3rd length C cells used in the original batteries.

    1. One method would be to mount the protection circuit in the tool. The makita handles are often hollow . I’ve been wanting to do this same thing with my stick battery makitas. Now if you leave batteries in the tool you would need to wire an on/off switch or somehow wire the board to be powered when the trigger is pressed (probably the most difficult but the most elegant solution). If you are willing to overvolt the tool (the motors in these tools are often rated for much more than they use) you can use a battery board designed for modern generic replacement packs. My favorite is the one designed for Milwaukee packs; it is cheap and readily available on sites like aliexpress.

  4. I have a Craftsman 18 volt drill and I hadn’t touched it in years and I picked it up and pulled the trigger Just for kicks and it turned a little bit I haven’t tried to recharge the batteries I wonder if a current 18 volt battery would work in it. My go-to is a set of rigid with the lifetime warranty.

  5. I have a couple of drills with dead NiCd batteries.
    In both drills, the batteries are inside the handle, and not quick change packs.
    I used them so seldom, that if I left them in the chargers, the batteries would go bad, and if I didn’t leave them in the chargers, they were dead when I needed them. Darned if you do, danged if you don’t. B^)

  6. Please please please do NOT use those shitty Chinese multi cell battery protection modules. They are total garbage. They can be easily recognized just by looking at the picture. If it shows separate protection IC for each cell dont buy them. Search for ones which have IC-s that handle multiple cells at once.
    Difference is that if an IC only monitors a single cell it does not (nor designed to) know that its part of a multi cell battery. If one cell goes out of control but the whole pack as a single entity is within spec then the “global” protection does not get activated.
    Also there is absolutely no cell balancing with these.

    You can find proper multi cell protection and BMS modules on ebay/aliexpress/”insert you favorite site here” .
    For example the ones which have the “BM3451” IC on them are (if they fit the bleeding resistors) are good. They cost only a bit more (like 10%), but that IC has all the functions necessary.

    1. Quality Chinese Engineering for the…loss.
      What he said. You don’t want to take chances with LiIon cells. The Benchmarq(TI) stuff is good. The Chinese stuff is not.

      1. That chip does not have balancing features, I would avoid that too.
        For example this one has the IC I mentioned before:
        If you want higher current out of these boards, just modify them. Replace the FET-s, change the current measurement (replace the shunts with smaller value resistors) or protection settings. Or just search for one that already rated for the required currents.

  7. When the batteries for our old 12V DeWalt drills at work went bad, I emptied out some of the old packs, added a cable with a 12V connector (for automotive accessory socket) and repurposed them as adapters for the drills we could use in the vehicles we worked on. Granted it turned “cordless” into “corded”, but a ready source of 12V was always right at hand without the hassle of swapping packs as they drained, and the cable rarely got in the way.

    1. One place I used to work at, had a battery packs that required a “reset” with a certain device before they would work.
      This was to discourage theft of the battery packs.

  8. Nice comment
    thanx for the info
    It’s funny, I did exactly the same hack 2 weeks ago and have not put a bms yet, I just checked and apprently my cheap aliexpress has the rigth circuit BM3451 in it.
    lucky me.
    Anyone has a good link to explain how to choose a good bms?

  9. After a few cycles of getting replacement cells for my now going on 30YO DeWalt cordless tools and my going on 20YO Makita cordless tools I am done with them. The aftermarket battery packs do not fit near as nice as the stock packs and my stock packs are cracked (they only stand so many drops, and if you use them a lot, they do get dropped dispirit your best intentions). I also have no desire to light my shop on fire with unattended chargers and the wrong technology batteries. Soo, the old tools get used less and less or are saved for the more,um, likely to cause damage to the took task, and I got new RIDGID tools with lithium batteries and a lifetime warranty on both the tools and the batteries. No need to screw around buying or rebuilding packs for the rest of my life. The new tools do not feel quite as nice as the old dewalts. This may be they are not as nice or I am just not as used to them, but they do pack a hell of a punch and are a lot lighter, and have some nice features. The little built in light for example is surprisingly handy.

  10. I know this will probably get an extremely negative response as it is “blasphemy” around these parts, but holy s**t, this is incredibly dangerous, and should be vehemently warned against rather than promoted. Before you write me off, please ask yourself: have you been in close proximity to a lithium battery failure that induced thermal runaway in a pack? Have you heard the sound of a blowtorch as the gas vents and ignites, followed by 10 foot long spark fountains rivaling commercial fireworks? Did you stay long enough to see the following explosions rip the aluminum enclosures to shreds?

    I’ve been working commercially on packs with this type of cell for years, and thermal runaway is no joke. No one should violate the rules about safety with these cells, especially without experiencing runaway firsthand.

    What has been done here is incredibly dangerous:
    1) Those cells *are* permanently damaged from soldering. Tabs are resistance welded or ultrasonically bonded for a reason. There is no way to solder to an 18650 without permanently damaging it, period. Will this damage be evident? Almost certainly not – this is why it is so dangerous. It will likely work initially and the damage is not visible, but I assure you, the cell has been damaged.

    2) Even worse, this was originally a NiMH battery, and that BMS is *not* controlling charger current or voltage. Virtually all NiMH batteries are rated for 0.1C (C = capacity rating of the battery in Ah) continuous charging current. This means they can continuously absorb current at 0.1C even at full charge, without damaging the cell. Lithium ion batteries exhibit internal crystal growth under these conditions. These dendrites can eventually puncture dielectrics causing internal shorts followed by thermal runaway. If it is used with the original charger, it will exhibit crystal growth that will result in runaway.

    3) By gluing them together rather than using a cell carrier, and by not leaving any gaps in the glue, there is no escape path for hot gasses if a cell vents, which almost guarantees runaway in that scenario. And a cell venting scenario is almost guaranteed, due to a charging plan that ensure dendritic crystal growth.

    This project is a fire hazard and literally a ticking time bomb. If you built 100 and left them unattended, I would expect many of them would result in fires. If you left them plugged into the charger, this would happen even sooner.

    Hackaday, please enforce a minimum standard of safety when posting projects that include 18650s. These things are way more dangerous than most people realize. I love this site, been to the supercon, but this is extremely disappointing.

    I also want to make it clear that I mean the project creator no disrespect. I soldered wire to NiMH, Alkaline, and Lithium-Ion batteries when I was younger and less informed. I never saw a runaway from these projects, though most of them were discarded in short order. That doesn’t mean any of them were safe – they weren’t. I urge everyone to exercise caution around these batteries. Buy them in small packs with tabs already welded. Use proper chargers.

    The best public facing 18650 safety test data I’ve seen comes from NASA.
    If you want to see what I mean about invisible damage to cells, take a look at the CT scans on pages 39/40 of this PDF. Look at the internal damage to the cells that were adjacent to those that went into runaway. Look at the distortion of the inner layers – this is heat damage.

    For more examples of the kind of propagation testing pack designers do, here is another interesting NASA presentation:

    For the most comprehensive and important information regarding designing a safe battery pack, refer to UL 2271:

  11. Thank you BMS Designer! I enjoy messing around with these battery hacks and have never had a problem. But you have made me more aware of risks I had not fully understood. Again, thank you.

    1. Dlfs, thank you for your kind words! These cells are incredible and I can understand why people love using them – I do too! I highly recommend you use cheap cell carriers such as the Keystone 1043 (mouser pn 534-1043) or similar. When designing a PCB to use an 18650, parts such as Keystone 54 (mouser pn 534-54) are a nice solution for a couple cells. Make sure to solder without the cells in place :) Note that keystone was just the first manufacturer on google, and I like providing orderable parts. Any other manufacturer stocked by mouser/digikey is equally suitable.

      If cells are:
      1) high quality original cells
      2) not heat damaged
      3) charged with the prescribed charge schedule to the prescribed voltage

      they are actually very very safe. however, you can violate all 3 of these and mostly be fine – this is how “hoverboards” were mostly fine except the few that were extreme fire hazards.

      Hackers absolutely still should mess around with 18650s! We should all just make sure to *never* solder to them, and always charge safely. If any of your projects violate 1, 2, or 3, you should seriously consider investing in a fire box to place the projects in. I’ve seen the corners of these doors forced open by lithium battery explosions, but never enough to cause a structure fire.

      Maybe I should make a post describing best practices around these batteries (referencing particularly interesting cells so people can actually implement)

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