Lithium Battery Pack Teardown

For reasons not relevant here, I tore down a battery pack containing three 18650 lithium cells. After a major struggle that involved drilling access holes into the side of the case and hammering the cells free of their silicone potting restraint, I was confronted with this:

Li-ion cell - unwrapped

Li-ion cell – unwrapped

Battery may explode or fire if mistreated. Yeah, that could happen.

Having pretty well ignored all the warnings, the damaged cells spent two days in the cold on the patio:

Li-ion cells - safety layout

Li-ion cells – safety layout

They seem unchanged, so I’ll dispose of them at the next electronics recycling event.

As it turns out, the gadget containing the pack subsequently died of a whoopise while trying to figure out how the pack’s boost regulator worked, so it joined the cells on the outgoing pile.

So it goes …


  1. #1 by tantris on 2016-01-19 - 10:30

    MIght still have some usable cells in there. I assume you measured the voltage. If it is close to 0V, you can try something like 3V-3.5V with low amperage, if it has a built-in safety thingy, I might jump back from 0V to around 3V.

    • #2 by Ed on 2016-01-19 - 12:46

      There’s Bad Juju in the associated gadget, so (quite atypically) I’m willing to be done with everything about it…

  2. #3 by david on 2016-01-19 - 18:40

    You think that’s bad, my next project looks like it’s going to involve a quad of these:

    • #4 by Ed on 2016-01-20 - 09:16

      Don’t drop a screwdriver across those terminals!

      • #5 by Vedran on 2016-01-20 - 10:50

        What screwdriver? Oh you mean this puff of smoke? :)

        I was building a 4S2P pack out of 18650’s the other day and got a little careless. Fortunately contact was very short, bot boy did it pop… I got scared sh$%&less :)

        • #6 by tantris on 2016-01-20 - 12:04

          Refillable pencil leads make great magic smoke. [br] I got the stupid idea from a science book for kids, so I could explain a light bulb: Two alligator clips in a mason jar with a pencil lead in between. They used a 6V lantern battery. I replaced it with a 18650 4S1P and wrapped the clips in aluminum tape, so they wouldn’t crush the pencil lead. A longer lead gives you a dim lightbulb that lasts half a minute. A short lead gives you a light bulb you can read by (for 2 sec…).

  3. #7 by Frans on 2016-01-20 - 15:35

    Slightly off topic, but it occurs to me that you might also enjoy this YouTube channel:

    (Hopefully the spam filter won’t eat it it. Fingers crossed. :P)

    • #8 by Ed on 2016-01-20 - 19:38

      Scanned the drill battery rebuild video: never knew the microcontroller would self-destruct when you remove / restore power. Doing a hot rebuild … yikes!

      • #9 by Vedran on 2016-01-20 - 21:56

        That’s pretty much standard for li-ion packs in notebooks and power tools. I’m guessing they’re selling it as a safety feature, but it’s just your classic highway robbery same as inkjet cartridges.
        Makita power tools for instance sell in two flavours: tool+battery pack and tool only, and the latter is usually half the price of former – OK, they might be using expensive Panasonic cells but still 10 cells shouldn’t cost as much as the whole drill. And their controllers are even worse – they allow 3 over-temperature events before permanently bricking the pack. Their chargers will typically do 2-4C charge cycles, so high temperature is not really unexpected. People who use them a lot know better then to immediately charge hot pack taken off the tool. Leaving it to cool before charging makes it less likely the controller will brick it.