DIY Battery Reconditioner Saves Old Rechargeable Batteries From The Landfill


Instructables user [msuzuki777] had amassed quite a collection of batteries over the years, but was finding that some of his rechargeable AA and AAA cells seemed to be at the end of their useful life. After reading some information at the Battery University regarding the restoration process for nickel-based batteries, he figured he might as well try building a battery reconditioner of his own.

He worked through several designs that either flat-out did not work, or had issues that limited the number of batteries he could simultaneously recondition. After reading about this rechargeable battery capacity tester we featured a few months back, he was ready to give the project one more try.

It seems that the third try was the charm, because his FET-based design worked quite well. He ended up wiring two FETs to each battery, which are connected via a relay. The batteries get discharged until the voltage drops down to 1V, at which point one FET is turned off, allowing the batteries reach their target voltage of 0.4V more slowly.

Despite the self-proclaimed messy layout of his circuit, [msuzuki777] is quite happy with the results. He has been able to recover several batteries, which is a fantastic alternative to letting them decay in a landfill.

20 thoughts on “DIY Battery Reconditioner Saves Old Rechargeable Batteries From The Landfill

  1. Is there no life on the battery it self after you’ve tried restoring it over and over again, does it eventually die completely not being able to hold a charge?

    Interesting none the less.

  2. You know what else saves my rechargeable batteries? Actually fully discharging them.

    When my phone shut off saying it had no battery left, I took the battery out and powered a bank of LEDs with it for 2 days straight. Once it was fully discharged, I put it back in and recharged it. That more than doubled the useful life of the battery.

    Whoever decided to put this ‘cutoff’ circuit in batteries that prevents proper charging is a complete idiot and should be electrocuted with AA batteries.

  3. Interesting, as I also have a substantial pile of used AA and AAA cells which hold about 20% of rated capacity.

    @M4CGYV3R Yeah, I have had this too.
    I’ve also had issues with Li-Ion phone cells not working at all (0.0V) due to the LVC turning on.
    The fix here is to charge it from a voltage limit of 3.3V until the cell starts taking a charge, then put it back in the phone- DO NOT do this with bare Li-Ions without protection boards however.

    NiCad and NiMH usually fail short in my experience, typically the +V end cell in a pack with model boat/etc packs.
    My theory is that the heat from the longer soldering causes that particular cell to degrade faster than the rest, which becomes even worse with RoHS compliant solder.

  4. @M4CGYV3R protection circuits are there to prevent lithium batteries from exploding due to complete discharge or overcharging

    the whole thing about phones turning off before the battery has discharged to the cutoff point is for additional safety rather than risk a protection circuit failure, which i believe was a contributing factor in those incidents with lipos made by sony

  5. also im working on a nicad conditioner that works on the idea of voltage surging, basically giving short pulses of very high current through the battery to shatter the crystal formations in the battery

  6. @Decius
    You are correct there is a finite service life even with the various conditioning regimes. The chemical reaction that powers battery cells is not 100% reversible even under the best of conditions. The conditioning just allows to to get closer to the theoretical maximum for a given cell type.
    I’ve been under the impression that Li based cells had a longer service life if you never allowed them to drop below 30-40% rated capacity. which is even above the cut-off for most control boards
    Doesn’t this technique only work on Lead-acid batteries?

  7. @abobymouse

    Ive seen that in some <20 year old CNC lathes and in the viscometers the company I work for makes. And given that I now have access to lacing cord, I can do cable lacing to my hearts content which I have been doing in my latest project (which I hope to get featured here when its done)

  8. @M4CGYV3R

    Discharging Lithium-(all chemistries) shortens the life of the battery. Most devices will stop discharging at 20% and stop charging at 80% to extend the number of charge/discharge cycles. Of course, the devices reports these two levels as zero and 100% respectively.

    Pertaining to the story, this is great. Now, someone just needs to build an uber battery checker/reconditioner for all battery types, including the high voltage high frequency lead acid reconditioning circuit.

  9. Nice, haven’t seen lacing like that in years. I had a bunch of lacing cord, but lost it somewhere, sad….

    One of these days I’ll build one of these, I have a serious need for one. Just no time….

  10. @Leithoa

    i have seen people recondition nicads by passing high current backwards through a battery pack (using a mig welder and tapping the contacts)

    i have a large number of packs i can test this out with, im going to use 12 volts at roughly 10 amps and see what happens, a few hundred millisecond pulses should work

  11. to all the people talking about NiCad current pulsing to kill off the dendrite crystals and restore capacity, it’s a short lived fix. HaD featured using a camera flash as the zapper a long time ago which is a fantastic way of doing it, but any form of zapping will leave the batteries with monstrous self-discharge rates.

    it’s cool to revive battery packs when you need them for a brief run or something, but once a battery has gone bad to the point of needing such drastic restorative measures you’re better off recycling it and getting a new one.

  12. im building my system to deal with a substantial number of nicad packs that have degraded or have gone bad due to student neglect or abuse in a robotics lab

    the batteries in question are trickle charged on a daily basis (slow charging speeds up dendrite growth) and are tethered to a power source whenever possible

    a faster discharge rate is worth not having to replace batteries every few years when our operating budget is as small as it is, being able to increase the lifespan of even a handful of the 50 or so packs i have in a box is worth it

    and that loom is pretty nice, another interesting method of bundling wire is to use a power drill to twist the wires together, works very well for thin gauge wire

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