Turn Cordless Tool Batteries Into USB Chargers

It is the unspoken law of cordless tools – eventually you will have extra batteries lying around from dead tools that are incompatible with your new ones. Some people let them sit in lonesome corners of the garage or basement; others recycle them. [Eggmont] was facing this dilemma with a Makita battery from a broken angle grinder and decided to make a USB charger out of it.

[Eggmont] took the simplistic approach, using an old cigarette lighter-to-USB adapter. First, [Eggmont] removed the battery connector from the bottom of the broken angle grinder. Next, the casing surrounding the cigarette lighter plug was removed so that the adapter’s wires could be soldered to the contacts on the battery connector.¬† The USB ports were then glued onto the top of the connector. The adapter was rated 9-24V input, so it was fine to use it with the 18V tool battery. Since the battery connector is still removable, the battery can be recharged.

Tool manufacturers are tapping into the market of repurposing old batteries for charging mobile devices. Both DeWalt and Milwaukee Tool have now created their own USB adapters that connect to their batteries. Or, you can purchase the Kickstarter-funded PoweriSite adapter for DeWalt batteries instead. Compared to their cost, [Eggmont’s] project is very economical if you already have the battery at hand – you can find the USB adapter for less than $10 on Amazon.

27 thoughts on “Turn Cordless Tool Batteries Into USB Chargers

    1. Most old tools use NiCd cells and worst ones even use NiMh which aren’t suitable for high current draw due to their high internal resistance. Turning the old packs to Lithium, if done well and keeping safety in mind, gives those tools a lot more energy density making them much more durable than new.

      1. I think you got the NiCad/NiMH resistance reversed, even though they are almost identical in this regard. The old tools used NiCad because NiMH wasn’t widely available yet. A NiCd tool can use NiMH as-is, but a new battery charger will be required.There may also be Lithium batteries for these same tools, but probably not (and they will also require a new charger).

        My old tools (NiMH) are used intermittently, so upgrading lithium based tools is not cost effective. I buy a new NiMH battery every 3-5 years.

        1. Unfortunately I was right, check batteryuniversity and other respected sources for graphs and data about internal resistance: NiCd are better than NiMh in this context and more suited for high current loads such as motors.

          1. Hybrid cars largely use NiMH and they seem to handle the high current just fine. (Though they’re definitely not ordinary off the shelf NiMH…) NiCd is supposed to have been phased out due to RoHS, but in practice, I have seen some 700mAh “NiMH” AAs (for use in solar garden lights) that I suspect are actually relabeled NiCds in order to evade RoHS…

          2. The internal resistance is per cell. If you have the ability to gang up multiple cells in parallel you can trade off capacity to increase the maximum current draw, which is fine for a car with lots of space for cells and a petrol engine to take over when the batteries are depleted. Handheld tool batteries don’t have those luxuries, so max current draw is sacrificed to increase tool runtime.

  1. Haha. I did this before the Ingress Helios event. My hack was special in that I used the copper connectors from a house receptacle to clip to the battery, so this hack could be replicated easily with a trip to walmart or home depot etc in an emergency. Robust reversible connections are good. Especially if your only charger is the original.

    I predict that LED flashlights and USB charge ports will come in the batteries in the future.

    1. “I predict that LED flashlights and USB charge ports will come in the batteries in the future.”

      That would be nice, but of course, the tool manufacturer will use yet another form factor for the connection. (sigh!)

    1. Most battery packs should contain industry standard cells like 18650. I have re-vived several tools over the years, it’s good to always have a ten-to-twenty pack of besaged cells lying around …

      1. They only sell the High Capacity or High Capacity Li-Po separately. And of course the kit comes with weenie saw, weenie drill and two low capacity li-ion batteries. (I bought one, it wasn’t a 1/2 drill, only 3/8 and it would run out of power if I tried to do any work with it. The $300 6-piece kit had low capacity Li-Po packs, but it is much better and a 1/2 drill)

  2. acomputerdog> Where do you get batteries that outlast the tool?

    Oh you do not want tools that crappy. You are going to have to start thinking of the batteries as consumables. Ebay is a good source of NiMH sub-C soldertab cells if you have the skillz to rebuild them.

    The drills themselves are amazingly tolerant of different voltage. I have a cordless drill that had built-in batteries I was gifted with 20+ years ago. I gutted out 5 leaking NiCads (~6.25 v.) and fitted a cable (later: Anderson powerpole) and ran the thing for years off of 12 volt AGM sealed lead acid batteries. Only do this if the only powered thing in the device is a motor. LEDs and lightbulbs won’t generally be happy with the extra volts unless regulated.

    @ HaD: search mojo: Mintybuck (and I’d bet he wasn’t the first to put a buck converter on a cordless tool battery)

    1. This is why I have a 14.4v dewalt drill that I converted to run off 18v black and decker packs. It’s truly an abomination. At that point though I thought it was useful to have a 2nd drill and I had several of those packs.

  3. In my experience, it always seem like the tools (or whatever) outlast the batteries. With lithium, there is a use case where the batteries have degraded to the point of being unusable in the original application but still be useful for less demanding applications.

    1. This is the case in which I’m interested. Seems to me those batteries that may not be able to hold enough charge to run a power tool should still be able to hold enough charge to do something useful (power a radio, a small battery powered lantern, etc.), especially if the voltage is dropped through a DC-DC converter.

  4. I use a PS2 power supply to run one drill, and an ATX supply to run another that has 3 attachments. Even those super cheap drills outlast their batteries. I have two small circular saws, Dewalt brand that will get the same treatment. Since I rarely am without mains power this is just free tools made to work again.

  5. Regarding battery failure and rebuilds. An 18V battery pack, built with NiCd’s, requires 18/1.2=15 cells. Such a pack has no intelligent circuitry, often nothing more than a inline fuse. No individual cell voltage monitoring or balancing is performed. It isn’t long until one cell gets far enough out of whack that by the time the battery is noticeably discharged, a cell is in full reversal. Then it typically gets placed on a dumb charger which relies only on a long, slow charge to at least prevent catastrophic damage; but it still isn’t doing the batteries justice. The higher the voltage of the pack, and the more cells in it, the faster it fails. Have seen these effects numerous times, in my handheld cordless tools, weed whacker, and even in $25,000 portable x-ray spectrometers at work. Replacing only the failing cell(s) results in more imbalances, setting up other cells to fail more rapidly. Replacing them all at the same time is fairly expensive, considering you’ll only get a fraction of their possible life.

    NiMH is more sensitive to bad charge/discharge practices, and I have no experience with large packs of this variety, as I’ve avoided them entirely for this reason.

    For the various lithium chemistries, dumb charging/discharging is too dangerous to get away with in a commercial product, so at least that isn’t an issue. Instead the pack life is limited by OEMs using cheap cells.

    I really wonder if a far superior replacement pack could be built by using just two larger cells of better quality, like the Headway 38120S LiFePO4 (3.2V 10AH, $19/ea), with a simpler two-cell battery management circuit. Then use a step-up converter to get the desired voltage. It would cost a little more and be larger than OEM replacement packs. But since the voltage can be adjusted, it would be a universal battery pack – rather than needing an 18V pack for one tool, a 24V for another, etc. It would have longer runtime than a typical battery pack (even with converter losses), sometimes much longer. And it would probably have about 5-10 years of usable life, before you have to spring for another mere $38 of batteries. If a four-cell version wouldn’t be too unwieldy, you could also power 12V devices like an inverter with it directly, with the step-up converter.bypassed; making it even more useful.

  6. I’ve often found that buying two batteries for a drill costs about as much as a package deal where you get a drill, two batteries and a charger, so I’d get a fresh drill mechanism and charger and keep the older ones a spare. I think I recycled most of the batteries, save for one to try a repair.

  7. Great for RV campers who depend on a pack full of USB rechargeable gadgets while boondocking. Desk lamps, lanterns, bluetooth speakers, tablets, bug zappers, shavers – the list is endless now.

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