Building A Cell Testing Station For 18650s

The 18650 is perhaps the world’s favorite lithium battery, even if electric car manufacturers are beginning to move towards larger cells such as the 21700. Used heavily in laptops and flashlights, it packs a useful amount of energy into a compact, easy to use package. There’s a small industry that has developed around harvesting these cells from old equipment and repurposing them, and [MakerMan] wanted to a piece of the action. Thus, he created a cell testing station to help in the effort.

Make no mistake, this is not a grandiose smart cell tester with 40 slots that logs every last iota of data into a cloud spreadsheet for further analysis. Nope, this is good old fashioned batch processing. [MakerMan] designed a single PCB that replicates the same cell testing circuit four times. Since PCB houses generally have a minimum order quantity of ten units, [MakerMan] ended up with forty individual cell testers on ten PCBs. Once populated, the boards were installed on a wooden frame with an ATX power supply which supplies the juice to run the system.

Overall, it’s a quick, cheap way for capacity testing cells en masse that should serve [MakerMan] well. We look forward to seeing where these cells end up. We’ve seen his work before, too – with a self-built laser engraver a particular highlight. Video after the break.

33 thoughts on “Building A Cell Testing Station For 18650s

    1. We’re those AA’s non-rechargeable alkalines?
      Because alkaline batteries have a high initial voltage, but horrendous miliAmp Hour capacity compared to even modern quality Ni-Mh batteries.

      1. AA alkaline still tend to have higher capacity. NiMH has kind of caught up to, but which is higher depends on which 2 specific models you compare.
        Where it will make a huge difference is if you discharge fast, in that case you will get more out of NiMH.

      2. The problem with NiMH batteries is that you pay for a rechargable battery but it only successfully recharges a few times before going bad. The old NiCds were weak but at least you could get a year or two out of them if you treated them right. But neither is really worth one’s time anymore with all the various Lithium batteries that are available.

        1. All of my NiMHs have lasted a long time with the exception of really old sets that were charged before I got a a decent individual-channel-per-cell charger. (In my case, a Maha MH-C9000)

        2. What? I have been using Eneloops for ages and they are great. Charging dozens of times so far, and some over 50. They are claimed to be good for 500 to 1000. Plus in storage they have 80% of their charge after a couple years.

      3. AAs actually have much higher mAh ratings, however they also have awful internal resistance so a lot of energy is lost to heat in high-current devices like flashlights.

        For high-current devices, the lower internal resistance of NiMH more than makes up for the lower absolute capacity.

  1. the problem with 18650 is that the majority of the ones are out there are fake… The printed (ie claimed) capacity can be a quarter (or less) of what it should be, and they can fail after 3 months anyway. I’ve tested quite a few, and then gave up buying any of the cheap ones – I’ve found a distributor that stocks genuine Panasonic ones (I’ve solidly tested them) and only buy those. Yes, they are a bit more expensive than the fakes, but they work! :-)

    1. This is one of the reasons you are actually better off using cells recovered from old laptop packs. The big companies have reliable supply chains so if it says Sanyo it almost certainly is. I seldom see a cell I recover at less than half rated capacity and often much better and no longevity issues in my experience.

      1. Indeed & FWIW, I’ve a few Ryobi cordless drill battery packs either 4 off 18650’s in one pa K for the older 12v style (previous NiCd drill type) or 10 off 18650’s for the 18v style Li-Ion drills. Almost 100% physically compatible ie the NiCd drill takes both the Li-Ion packs ie, just shave off a bit of plastic on edge of battery pack and all are compatible tight enough, just be careful drawing heavy power from the 18v Li-Ion pack through the 12v drill, don’t want to burn the brushes as they are getting old anyways.

        Thing is the Li-Ion packs have low volt protection and not just on discharge but charge too, if left on shelf not used for long periods in that the 18v 10 off 18650 total drops so the charger won’t even trickle it up to some normal range charge voltage to then charge properly…

        One particular 18V Li-Ion pack completely dead, so took it apart and sure enough all cells showing only about 50mv. So individually charged each at 250mA to just over 3.2v then put back in charger and voila they charge just fine. Have since used it several times and works a treat so far for months :-)

        Thing is I don’t have a Ryobi Li-Ion charger pack, only the oldie 12v (unfiltered ie rippled) NiCd one so modified it with a switch on output transistor etc to give out a bit more volts so it charges the 4 pack Li-Ion to just on 16v and works fine. Oddly it also charged the 18v pack without further mod as well but never more than about 80% charge but, I don’t care as hardly use it away from lab/workshop. So I now have 3 off Li-Ion packs 2 at 16v to the one fat one at about 19.4V or so all work great with the 12v NiCd drill. Still have the NiCd pack somewhere if need b.e.

        Only drawback is need a thick rubber band to hold the packs securely onto the drill base. Maybe the drill could do with a lube and brush service woon, it’s been going strong for over 5 years only slight gear noise but unwelcome as if grinding when on heavy load which isn’t often fortunately :-)

        1. @MikeMassen, I have exactly the same problem with my Ryobi 18V Li-Ion pack. Did you disconnect the cells before charging individually? If I remove the cells I’m scared the IC in the pack somehow realises and goes all DRM on me or something.

          1. I got a hack for you that has worked for me on Milwaukee batteries. Just bridge a garden variety 9V battery onto the positive and negative terminals of the battery pack. It forces enough into the pack to get the voltage to a point where the charger will accept the pack. Do this outside just in case something decides to go ballistic but it has always worked for me.

        2. At 50 mV I would definitely just discard those cells. What I have heard is that if cells go way too low they become a serious hazard to recharge. 2.5 volts is probably a sensible discard guideline. Charging cells that have sat at low voltage for a long time is Russian Roulette. Not that I don’t play, but just sayin’

    2. The first step is to weigh them and compare to a known unit. I got some that were too cheap to be true to test. Well, I never tested because they were about 1/4 the weight they should be. I opened one and it had a very short undersized roll. Now if I ever need to save weight in something with 19650 battery holders I’m golden!

  2. Good to see work being done on this, thanks for post :-)
    Would be great to identify and test batteries according to more than the base criteria of amphr capacity such as with either a stick on barcode generated each time with history index stored offline too or even laser etched barcode on body of unit and maintain its history over multiple usage periods as well as means to match up strings of series and parallel batteries where appropriate…
    Of course there are bound to be semi automatic means to provide dynamic matching too, much easier of course in static power wall type configurations :-)

  3. On the plus side, this is a good, uncomplicated way to check the condition of many different salvaged batteries and get an idea of their condition and capacity. On the minus side, this video gives me a headache. Can’t even pause the video to read clearly the LED readouts or the wiring details. The author should slow it down just a little bit so us old-farts can follow along without getting vertigo. Also, while I respect that different people have different tastes, IMHO this video is a good example of why God invented mute buttons – no disrespect intended :>). As for 18650s generally:

    . The different brands and types of 18650 cells all have different internal resistances meaning that they will discharge and heat up at different rates within the pack. Only the same model numbers should be used within a single pack and even that should be monitored closely as you don’t know how old they are (if salvaged from laptops, etc), and used batteries of the same brand will age at different rates depending on how old they were at the time they were manufactured. I therefore only use new batteries from a reputable dealer as it’s the only way I can gauge with any degree of certainty the overall quality of the packs I make.

    . As someone else noted, there are MANY counterfeits out there and it is common to rewrap old or lower quality cells in new shrink wrap copying the part numbers from legitimate manufacturers such as Panasonic, Sanyo, etc., in order to get quick sales of “new” but completely untraceable cells. You can literally peel away the outer shrink wrap and see the old part numbers printed underneath these batteries. Some companies try to brand their cells into something they’re not by making outlandish claims as to their capacity knowing full well that most people won’t bother to test them. I know of no official organization that checks the quality of batteries coming from these resellers so it’s literally Buyer Beware.

    . Li-Ion battery packs should be balance charged to get top performance and long life out of them. If they are not you run the risk of over-charging some cells and under-charging others within the same pack. Charging them individually, as is done in this video, is not a problem, but charging them en-masse within a pack is, which is why you should always use a BMS or balance charger to prevent your own charge routines from ruining the life of your packs. A BMS will allow you to use a standard charger safely – a balance charger requires sense wires attached to each cell group, but they are both well worth the investment.

    1. I noticed this too. I’m working on a project that will later need a current sensor and I haven’t yet searched for anything like a current sensor and yet I’m already seeing ads for these.

      It shouldn’t be surprising though, Facebook with advertise wedding fashion to friends of a woman who doesn’t yet know she’s pregnant.

      There’s definitely been an improvement in the AI behind advertising lead by google.

  4. A long time ago such batterry recovery still made sense. Now i see prices under 3 euro for brand new cells (Samsung, 2.2Ah, for quantity of hundreds).

    With many laprops having dropped this format, does such a recovery process still make financial sense?

  5. Well sure Bob Adamski,
    Though in relation to hackaday here which is electrical/electronic for the most part it’s broadly not that much context sensitive and not that specialised re Li-Ion with those in the industry ie power sources for projects. The peer reviewed scientific paper ‘standard’ (at least) is to put the new term with first char capitals of each word then put brackets around the acronym afterwards. Of course a glossary of terms helpful before index.
    Eg Such as Nickel Cadmium (NiCd) then just use the short cut ie NiCd but, that’s generally for more specialised environments where audience could be rather more diverse fwiw in biochem eg SOD1 in food chemistry has significance in copper enzymes in immune function and prion interactions.
    In this electronic tech situation with Lithium Ion (Li-Ion) batteries it’s far more widespread in that it hasn’t been that specialised an industry for almost 15 years or so, so I guess the vast bulk of people can recognise 18650 in mm is two dimensions concatenated much like 1206 etc is for Surface Mount Devices (SMD) conventionally in milli-inches.

    Are you new to this field of endeavour ?

    Can you be more specific ?
    As it is possible some acronyms obfuscated by bleed through from misunderstandings arising from misuse by those not writing in English which amusingly offers Chinese Whispers like paradigm, seen this in other countries too many amusing, some can be really tragic especially Material Safety Data Sheets (MSDS) issues re poisonous or carcinogenic materials where arbitrary acronyms could be downright dangerous when misread or used out of context with unintelligent lazy assumptions. Gene Dobri…

    1. “The peer reviewed scientific paper ‘standard’ (at least) is to put the new term with first char capitals of each word then put brackets around the acronym afterwards.”

      That’s the standard for ANY technical writing and the widespread failure to do that is one of my pet peeves.

      1. Sadly this site is far from any technical writing nor scientific in some case. You are lucky if the writers actually uses units correctly – correct upper/lower cases where they have different meanings e.g. b(it) vs B(yte), using correct units for things e.g. none of the football fields nor F(ailure) units for temperature, distances, weight etc.

        It is easy enough to hyperlink acronym to what they mean these days, so that’s an easy way to not distract away from being a big dictionary paragraph. Fail to do so is just laziness and not taking writing seriously.

  6. Three days ago spent way more than an hour to test 16 batteries and get 2 of six of them to have something close to nominal value…I’d pay at least 25 bucks for one of these. Buy three get one free would be good too.

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