laptop battery test question

Batteries and Chargers Rechargeable Batteries
1

I recently scavenged a laptop battery pack to see what sort of treasure was inside. I found a 3S2P 18650 pack with a PCB connected. I am only interested in the batteries for now, so I cut the PCB off and decided to investigate the batteries. I don’t own a battery analyzer, but I do own a power supply and a DVM. I measured the 3 sets, two were at around 3.5V, and the third was at 2.0V. I charged the pair at 2.0V up to about 3.7V and have let them sit. It seemed to me that it did not take many amp-hours to charge this pair up, so I paid a bit more attention while charging the next pair. I was able to add about 0.2V to the battery resting voltage in about 2 hours with a charge current of 0.27A. The original capacity of the pair should be 4 amp-hrs, and I added about 0.6A-hrs (a bit less) , or about 15% best case. I know the discharge curve of Li-ion is not linear, but roughly 0.8V is the usable voltage range, and to charge up 0.2V of that should take closer to 25% of the amp-hour rating, and that ignores any heating loss or other inefficiency.

Seems like these cells are likely no where near 2 amp-hour each any longer, which is probably why they got dumped. Is this a correct conclusion, or did I over simplify this?

2

I’m no expert, but I’ve cracked open 3 laptop packs—2 Sony VAIOs from around 2004 and my HP pack with LG S2s.

The 16 Sony cells are dated coded at 2002, so they’re 16 years old and have about 75% of their ~2000-2100mAh capacities. I’ve had them out of their packs for over a year and even charging them up to 4.2v, they settle at about 4.14v-4.15v after a week, but will generally stay there for a month, or three, discharging slightly.

4 of the 8 LG S2s (dated 11/2006) were down at about 2.00v, like yours, but I decided that I wouldn’t muck with them. The other 4 were at 2.90v and I salvaged them. They’re ~2100mAh and behave like the Sonys, so usable.

Why are you only charging them up to 3.70? Is it where the charger terminated the charge, or were you just being cautious?

Try charging them up to 4.20v and then let them sit for a couple/few weeks and monitor their voltage. If they settle down to 3.7v after a week, or two, then they might be toast, but if they hang above 4.10v after that stretch, then you can use them in moderate loads.

I’ll charge mine up at 1A, then I’ll use them in my lights that don’t bang hard on cells, like my Convoy lights with 2.8A driver boards, but only on medium and low. Frankly, they might be able to handle the 2.8v, but I don’t need to use them at that current rate.

Remember, laptop pulls used for any length of time, are ‘tired’ cells, so treat them with ‘kid gloves’.

Buy an inexpensive analyzing charge and do discharge tests at 1A and see what they have left.

Chris

3

Personally I stay away from ICR based cells. They’re the most volatile of Li-ion chemistry, and are dangerous in high drain lights. They can only handle 5 Amp draw max. Anything past that and you might as well kiss your hand goodbye, or at least lose a couple of fingers.

4

I have some Sanyo R1112 and LG cells from laptops.

So far. they’ve been fine on any torch with single cell,
With XM-L2 and under in there.
I don’t use any torch on high\Turbo,
apart from several second bursts.

Charged to 4.2v in XTAR VC4. 6 days ago.

Panasonic 18650B =4.2v 5 months old from new.

LG x 2. =4.10\4.11v Age = 4 yrs laptop. 3ish yrs out.

Sanyo x 2. = 4.17\4.18 Age=?? plus 18months here.

Only detriment I can find with the Laptop ones is the 2100 \2200mAh capacity. OK for inside torches though.

I just use the 3000+ Panasonics for 2 and 4 cell torches outside.

I’ve opened 5 Laptop battery’s so far. 4 x 6 cell.1 x 8 cell,
Only had one dead cell in all of them. (2.4v)

So for local\inside basic torches. I can’t see any problem with second hand cells.
as long as you use a decent charger. and be sensible with them.
They’d have to be better than the chinese ones in general.

5

As to why I am charging them (presently) to only 3.7V, I am using an old DC power supply current limited at 0.27A. A pretty slow process which requires a bit of monitoring. Which brings up the next point, I certainly do need some sort of proper single (or multi cell) 18650 charger, and one that analyzes could not hurt.

I will give them a go charging up to 4.2V or so and let them sit. Just will take a bit of time. Was wondering if the time was worth it, but I guess the only way to really know is to run a more quantitative test than I have. That’s were the analyzing charger would be the most helpful, but I may use some of the things I have on hand.

Long term I will pick up a charger, but was also thinking that the charger would be a lantern like this: *BLF LT1 Lantern Project) (updated Nov,17,2020) . I figured I would need some 18650 cells for it, and when I came across the laptop pack figured it would work for starters. The light will not demand high current best I can tell from the thread.

6

That’s interesting, but in today’s world, you can get a quality single bay charger like the Liitokala 100, or the Xtar MP1+, or MP1 ANT (volt meter on board) for under $10 delivered and these will all charge with proper CC/CV charging algorithms. With 500mA/1000mA charging rates, each is good for all but the smallest li-ion cells and even then 500mA will work. The Liitokala will also charge up NiMH batteries, like the Panasonic Eneloop.

For $30-$40 delivered, you could buy an analyzing charger and then ‘know’ what your batteries and cells are doing, removing the guesswork.

Anyhow, good luck, but if you’re going to be fiddling with this stuff and you’re going to be cracking open older battery packs, you really should be using a capable/safe charger.

You can peruse HKJ’s battery/charger testing site for a few weeks. Pretty much everybody who is anybody sends their crap to him for testing:

https://lygte-info.dk/info/roundCellChargerIndex%20UK.html

Chris

7

8

I think he forgot to mention they might give you AIDS and give your kids cancer if you use them above 5 amps.

Most of those old laptop cells are generally rated between 4.4 and 5.2 amps continuous current. So, while you shouldn’t use them more than 5 amps, they are required to pass safety tests such as shorting them. Shorting will ruin the cells, and likely cause them to vent, but it’s not supposed to blow them up or catch them on fire.

Luckily, you’re not likely to push them higher than about 4 amps in any flashlight, unless it uses a boost driver. When used in direct-drive lights (like most high-output budget lights), the voltage sag will limit the amount of current the LED can use to about 4 amps. And that will fall as the battery depletes.

So, yes, as long as they are in good shape, they’re safe to use in flashlights. You won’t get the best performance from them, compared to a new high-drain cell, but they still work pretty well.

But do get a proper charger! Even if it’s only a $5 USB charger, it will do a proper charge. Charge them up to 4.2v (using a proper CC/CV charger), and monitor them over a week. They should stay above 4.15v if they’re still good cells.

9

Yes, I will get a charger, but for now I am experimenting with what I have. My cells are rated 4A continuous, but I don’t plan on using them anywhere near that, just for the BLF lantern perhaps.

10

found a second pack yesterday, the purple samsung ICR18650 - 26H. These were all at 3.5V (4S pack). Charging them with my Olight charger for my S1R, We will see how these do and eventually I can do a bit of discharging to see how much capacity they have left. I like these better as candidates to use with the lantern.

11

So 10 laptop pull cells total charged, all of them charged to between 4.18 and 4.22V. The variation is due to the charging process. My Li-ion charger, which came with my Olight S1R, charges a bit on the high side. So I discharged the laptop cells all a bit to be near 4.2V on my DVM. Best I can tell using a calibrated meter at my work as a reference, my DVM reads roughly 0.05V high. So when my charger charges a cell, it reads 4.29 - 4.30 V on my DVM when the charges says it is complete. I am thinking this is really 4.24 - 4.25V. Definitely on the high side, but in tolerance. I usually take my Olight S1R off a bit before the charge is complete by monitoring the current into the cell via a USB current monitor. For these laptop pull cells, they charge much longer due to the higher capacity, and I did not monitor them during the charge as closely.

Anyway, I will keep watching the cells for a few more weeks, but it appears they are all likely usable for my intended purpose, which is the BLF lantern in the works. That is assuming flat top cells will work . . .

I know, get a proper charger, well the long term plan is the lantern will be the charger also, and then, at least for now, I don’t feel the need for a fancier charger. My only light that presently uses lithium is my S1R.