Laptop battery repair

I’m not sure if anyone here would find this interesting, but I decided to take apart a dead battery pack today... I pulled out all the individual cells and they’re all reading at 4 volts, which honestly seems fantastic on paper, especially since having six of them should give me a total capacity of 24 volts... so I can't quite wrap my head around where things went wrong, because the charger won't even touch it and just keeps insisting the battery is completely empty... I'm starting to wonder if the internal circuitry has simply fried, and if that's the case, is there actually any way to salvage this, or am I just looking at a paperweight...

Maybe there was a bit of a mix-up with how you measured things, or perhaps the connections aren't quite seated right. Honestly, I don't see how that would be worth the hassle; I'd imagine a battery like that wouldn't run you more than about $200-$100.

We’re talking about those 18650 cells, which can run you anywhere from $50 to $33 per unit if you're actually buying from a reputable brand or a legitimate dealer. On the flip side, you can grab the exact same models for just $20 to $13, but let's be real—they're either cheap knockoffs or they've already been cycled to death. That’s the magic of shopping on eBay, lol.
So, go ahead and try to do the math on whether that's actually a deal!

PS - You really shouldn't trust that multimeter !!!!

A multimeter is great because I use it to check standard batteries all the time, but I’m just not sure if the same logic applies when dealing with Li-Ion cells... specifically, I'm wondering if I should be measuring the amperage instead, and if that's necessary, what's actually the best way to go about measuring that accurately?

Sam Murphy said:A multimeter works fine since I use it for standard batteries, but I'm not sure if the rules are the same for lithium ones. Do I need to check the amperage, and if so, how would I go about measuring that?

Just measure the voltage exactly like you would with any other battery.
With Li-Ion batteries, each individual cell should sit at 3.7V, so a 6-cell setup ought to give you 11.1V.

Alexander Smith69 said:You just measure the voltage exactly like you would with any standard battery.
With Li-Ion batteries, each individual cell should ideally sit at 3.7V, so if you have a pack with 6 cells, you'd expect to see about 11.1V total...

The thing is, when I check them individually, they're all reading 4.1V. I actually pulled a few of them out to test them myself, so I'm wondering, what on earth could that mean?

Sam Murphy said:I'm getting 4.1V on each one individually after taking a few out to test them. What does that imply?

The nominal voltage should be printed right on the cell, usually labeled as 3.7V or 4.2V.
Typically, the total voltage for a 6-cell pack like that ought to be 11.1V or 12.6V.
If you're seeing anything less than that, there's likely a faulty cell in the mix or your connections aren't quite right.

Alexander Smith69 said:It’s probably a good idea to label each cell with its nominal voltage, usually something like 3.7V or 4.2V.
Generally speaking, if you have a 6-cell battery pack, the total voltage should come out to roughly 11.1V or 12.6V depending on the charge level.
If your readings are coming in lower than that, there's a high chance one of the cells is shot or maybe the wiring isn't quite right...

Everything looks solid on the assembly side; I actually took it over to my mechanic today to double-check, and all six cells are reading at 4.1V, but we really won't know the truth until we see how they hold up under load—we're planning to test them against a 50-watt automotive bulb...🍿, and if the voltage drops below 3.6V during the process, he thinks they're officially toast, and man... lithium is such a headache...🙂