Is this HP laptop battery — that has been fully drained — safe to use?

Question

I have a HP laptop battery model number MO06. I used it for 3-4 years and it was down to 50% capacity. After HP’s recommendation to discharge it fully and let it sit for a few hours, it killed it. So I replaced it.

3 years later, I’m reading about how some of the cells are still good in such cases b/c it is 2 in parallel and 3 sets in series. If one set of parallel is bad, it will trigger the onboard control to make it faulty. I use a volt meter on this 7 yr old battery, 3 of those years it has been empty and sitting on the shelf. They should be dead. However, 2 of the pairs still have at least 4V, while 1 pair is dead. (I should mention they are the 3.7V, cap at 4.2V. ICR18650)

Are the 2 pair ok to recharge? They both have 4V, but as I’ve said, I discharged the battery 3 years ago. I don't know why they still have a charge. Some of my more recent batteries on other laptops are showing 2-3 volts and they barely hold charges.

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I did more reading and I think I got a clearer understanding of my situation. I’m wondering if some people can verify my research? Mostly from Battery University and other sites, I’m not sure how reliable they are.

1. So first is the unbalanced capacity/voltage. In a typical 6-cell laptop 18650 battery, all it takes is 1 cell in a parallel to drop below a certain voltage for the whole battery not to work. Also, the damaged cell will lose capacity and unbalance the discharge/recharge. It means that it will reach 4.2V while the others are not fully charged or it will drop to 0 volt while the other 2 are still holding charge.

   In this case, it looks like what happened to my laptop battery. It always charged to 100%, but dies at 60%. It won't let me calibrate or update the battery health.

   If this is true, it would explain why 1 of the parallel cells shows 0V while the other 2 still showing 3.9V.

2. If the above theory is correct, it means these 4 cells, in 2 parallels, were actually holding 50-60% charge, which according to Battery University is the optimal storage charge with minimal capacity loss. They reported lithium cells have a shelf life of 10 years with moderate capacity loss.

From BU:

“There is virtually no self-discharge below about 4.0V at 20C (68F); storing at 3.7V yields amazing longevity for most Li-ion systems.”

“At 40 percent charge, most Li-ion has an OCV of 3.82V/cell at room temperature.”

Currently the 4 cells measure at 3.9V, I don't have a digital volt meter, so it is around there. This would support the theory in #1, these cells were in fact, holding charge around 50-60% and barely self-discharged in 3 years.

If this is true, not only are these cells good, they're not even in sleep mode.

Can I get any verification?

Thank you.

Answer 1

I have no idea why HP would have told you to run it down to zero - that killed it.

Basically, once an Li-ion battery drops to zero charge, that's it. It is not safe to attempt to re-boot it. The onboard controller will have shut it down.

A professional could try re-boot it using a much higher initial charge, but this is definitely not something to attempt indoors at home. The scare stories of Li-ion batteries going off like firecrackers are not exaggerated. Bypassing the controllers by splitting the cells into their component parts is not even vaguely safe: even if successful, what would you have gained? Half a battery.

Send it to the recycle and buy a new one.

Answer 2

Ok, after lengthy research and conversations with many people from many sites, I have concluded my investigation. These are the results.

1. Laptop batteries are comprised of 18650 cells in parallel sets connected in series. Their capacity wear and tear is based on only "1" of the cell pairs. If 1 cell pair dies, the circuit will render the battery useless. If 1 cell pair drops to 50%, they all will be limited to 50%, even the 2 good cell pairs.

2. Voltage IS the easiest measurement of a cells capacity level, but as stated by others in this thread, load matters. A cell with less capacity will reach 4.2V "faster" than other cells. Once it reaches 4.2V, your laptop will stop charging ALL cells. When drained and without load, it can still show 3.8-3.9V. However, under load it is typically 3.6-3.7V at the empty end.

3. From 1 & 2 above, the bad news is, the bad cell pair will keep degrading b/c they'll be pushed to 4.2V max voltage tension. The good news is the other 2 cell pairs will have life extended b/c they're charged to only 50% capacity, which is the ideal capacity for storage. This means, you CAN salvage the other 2 cell pairs if you want to use them for future packs etc... even after the bad cell pair eventually dies.

4. If your battery can be charged to 100% but only discharges to 50% before suddenly shuts off, it means at least 1 of your cell pair lost capacity to 50%. If you do not want to calibrate, set your Windows critical battery to 55%. The benefit of this is, if you completely drain the battery (according to the battery meter), only the damaged battery will drain to your critical level, the other 2 cells will remain at 50% and above. A battery that suffers major wear and tear has a good chance of dying if it is discharged too low. In such cases if this cell pair dies while in operation, your whole battery is useless and your 2 good cell pairs will be left at 0%. If you want to salvage the other 2 cell pairs, it is better they are at 50% level rather than 0%.

5. However, in 4 above, this also means the 2 good cell pairs will be running at 50-100% while you still use them. It means if you are plugged into the AC most of the time, their voltage tension is at 100% and that continues to accelerate their own wear and tear. So the alternative is to calibrate your battery, then it will start all 3 at 0% and charge to the highest of the damaged cells at 50%.

6. To answer my own question. My 7 yr old MO06 cells, the 2 cell pairs are probably good. However, I cannot remember if I calibrated them before they died. So they may have been holding 50% and self-discharge in the past 3 years or they were empty these 3 years. Their voltage holding at 3.9V indicates they are good batteries, all my other cheap worn batteries are below 3V. According to many sources, they're not even in sleep mode. Sleep mode is triggered by low voltage.

   However, this is not under load, so when charged up, it is likely they lost a lot of capacity in the past 3 years. So even if I am to charge them, it is likely they will not hold as much as before and would not really be worth it. They may very well be at 50% capacity by now. For a average user, this is not worth it. (BU's information on lithium is wrong, they meant primary lithium not rechargeables. Primary lithium can be stored for 5 years with lost of 10% capacity. Rechargeables, good ones, lose about 5% charge every month.)

   If you are one of those people who collect these things for projects and salvage, I think these 4 cells are excellent top grade to be salvaged. Even my current battery, 4 cells are also excellent. But from what I've read and researched, people who do this have external chargers and there is a procedure. It doesn't make sense for me to buy a charger just for these cells when I'll only be doing this once every 4 years or so. Not to mention if I am rebuilding this pack, I'll always be using cells from the previous battery, which will have an age of 7-8 years.

   It is also better to have a charger to charge these lithium cells individually. If you plug them into your laptop with the other cell pairs in series, they have to match voltage. If not, you have to calibrate them, which is to discharge them to empty before charging back up. Again, bad thing to do to an aging lithium, by doing so you may have just killed them again or lose even more capacity.

7. Buying good batteries. The OEM Duracell Mo06 batteries run at $120 and has a life of 3-4 years. Originally eBay imitations were $30 each, with a life about 1 year. So the price was about the same, that was why I bought the Duracell.

   Do NOT buy the $12 ones. I realized the prices on the generic did not actually drop, they're still there for $30. The $12 are not simply generic, but they're cheap quality. I actually have one, it came dead. I opened it and checked. The circuit board was bad, the cells were bad. Not just that, they didn't have a fuse. They actually shorted it b/c a fuse costs $2.

   The vendors for the $12 batteries are ALL THE SAME. If you look at them, they use the same pictures, same fonts, policies, etc.. word for word. They even ship from the same location. They all have the same rating as well. It is the same company or group of people under the different accounts. When their account drops below 99%, they close it and open a new one. The ones I'm looking at are all 99.1%

   You also need to know, many people if they get bad product, once they get a refund, they do not leave rating for them. Many already don't b/c out of fear of retaliation, so the ratings are typically higher than they should be.

   If you do not want to spend $120 on a OEM new battery from a known brand, many of the $30 eBay ones are generic but have manufacturer's name. This is a little better b/c at least you know it has a name, better than nameless. Many of them list one important thing, it comes with a fuse protection. Of course they may lie and unless you pop it open to check, you wouldn't really know. But if you check the vendor, making sure his ratings are not the "same" as the 5-6 other ones, you know at least this is a "real" vendor.

   I have 1 laptop battery from eBay which lasted one year. With my recent project, I popped it open and was impressed. Not only did it come with a fuse, but the circuitry even came with a 2ndary LED panel which shows up on the top cover so you can see the battery level. This is for an older laptop and my current generic one didn't even have this feature. Surprisingly though, the current one is going on 2 years at only 30% wear and tear. That's pretty impressive for a $30 eBay battery.

Conclusion:

Anyhow, I hope this has been helpful to anyone in similar situations concerning laptop lithium ion batteries. Frankly speaking, I think the technology is stupid. They are designed not able to charge and discharge individual cell pairs, so basically wasting 2 good cell pairs when one went bad. There should be some sort of voltage balancing in the circuit.

I read and watched youtube on new companies designing new batteries that are doing exactly this. However, I don't think they're doing it for laptops, mostly for other things like electric cars. I guess for cost reasons, it just isn't worth it. This is why people are trying to recell their laptop batteries. Instead of replacing with $120, you can buy 18650 cells and replace the bad ones for $10 ($5 a piece).

But again, unless you're an engineer who is really into this stuff, it really just isn't worth the trouble. $120 for a battery that lasts 4 years is not that bad at all.

Good luck!