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I am in the process of changing the battery cells in my laptop battery pack and have to somehow connect lithium ion cells. I unfortunately do not own a spot welder and buying/making one for this project is not worth it. Soldering is obviously not an option because of the heat.

While doing research I stumbled across this video.in which he connected several lithium ion batteries using electrical tape and wire.

How effective is this? The batteries won't be exposed to that much stress.

Additionally how safe is it to reuse old lithium ion batteries? They are taken from an old laptop from 2012. The voltages are all fine (ICR 18650 30B with measured voltage of 4.23) but I don't want them exploding or burning. Will using tape increase the risk of failure/disaster, maybe increase the heat?

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That video is only good to show that wires can connect things. It is not a good way to connect batteries, especially if you need the pack to last. As the tape slides/stretches, then the contact resistance of the wire will change between cells. Potentially even opening.

You are better off ordering batteries that come with solder tabs

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    \$\begingroup\$ Strongly agree. Typically, there is contact welding apparatus in notebook repair workshop. Cells in battery should be checked to have same capacity and series resistance. Do not skimp on this, good cells are not cheap, but will work for years and will not explode. \$\endgroup\$
    – Vladimir
    Commented Jun 27, 2022 at 17:13
  • \$\begingroup\$ And check eBay for cheap spot-welders. They exist.... \$\endgroup\$
    – rdtsc
    Commented Jun 27, 2022 at 17:58
  • \$\begingroup\$ The tape stretching won't really be a problem because of the right fit: picture of laptop battery. \$\endgroup\$
    – iohn
    Commented Jun 28, 2022 at 8:50
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I would be very suspicious of 10 year old lithium laptop batteries. I've dealt with thousands of lithium ion batteries, 10 years would be seriously pushing the limits, usually you're lucky to get half of that. When you measured the voltage did you have a load connected? Battery voltage is almost never a good indication of condition, a bad battery can measure full voltage with no load but as soon as you draw current from it the voltage drops significantly.

As far as using tape to connect wires to them, not a good idea. A loose or oxidized connection will create a resistance, resistance and current cause heat. Drawing amps of current through a poor connection can cause enough heat to be a fire or explosion hazard, especially when lithium is involved.

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  • \$\begingroup\$ I measured the voltage under load with a 500 ohm resistor and got a voltage of 4.23 on the good ones and 4.22 on some other. The battery in question is link has two voltages, nominal (3.78V) and charging (4.35V). Are they still functioning or are they bad? \$\endgroup\$
    – iohn
    Commented Jun 27, 2022 at 20:57
  • \$\begingroup\$ @iohn 500 ohms is only going to draw 8.46mA, a small fraction of what a laptop will draw, so it's hard to say how they'll work powering one. Are these cells that you purchased that are supposed to be good? \$\endgroup\$
    – GodJihyo
    Commented Jun 28, 2022 at 1:53
  • \$\begingroup\$ These sells are the ones salvaged from the 10 year old laptop. I know that they charge but did not test how good they hold the charge. I now tested with a 300ohm resistor (the smallest I can make) and got the same results. \$\endgroup\$
    – iohn
    Commented Jun 28, 2022 at 8:51

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