Aftermarket Li battery components

Hi,

A friend just gave me a couple of "expansion batteries" for my tablet PC's. Of course, the batteries are flat.

*And*, of course, they won't take a charge. :<

Pulling one open, there are 4 (5?) batteries that appear to be identical distributed around the case (the battery pack is very thin but as tall and wide as the tablet).

Is it worth trying to replace these with some comparable cells? (I am sure the vendor of the original expansion pack would charge a heavy premium to put those cells in this large plastic shell and resell it! :> )

What other issues might I have to worry about?

Or, is it better to just live with the standard (working) batteries and discard the expansion batteries?

Thx,

--don

Reply to
Don Y
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This is a complex issue. Words like "flat" and "won't take a charge" may be clear in your mind, but don't communicate much.

I've spent considerable time working on this issue.

The executive summary is, "give it up and go do something fun."

If you're gonna mess with this, there are some ground rules.

WEAR EYE PROTECTION. DO NOT SKIP THIS STEP. I'VE HAD NiCd BATTERIES EXPLODE AND SPRAY HOT CAUSTIC STUFF IN MY FACE.

Don't let your kids watch. Don't leave it unattended. Have an EMPTY metal trash can handy and a clear path to outdoors. Make sure your fire insurance is paid. Have a working fire extinguisher handy. It won't do much for a lithium fire, but might keep the whole house from going up.

NEVER, NEVER, NOT EVER SHOULD YOU SOLDER DIRECTLY TO A BATTERY. Repeat that until you believe it. Don't let anybody tell you otherwise. Let them blow up their laptop if they want.

My experience is mostly with packs over 5 years old. Protection circuitry becomes progressively more sophisticated.

I've experienced two failure modes.

1)cell is open. The pressure switch has opened and they ain't coming back. 2)High internal resistance. The amp-hours are in there, but the protection circuit or the laptop won't let you take it out.

Of course it's possible that your cells are good and have just overdischarged and the electronics have disconnected 'em.

You've got it open, check the voltage of each cell. If it's over

2.5V, you can probably charge each one individually to some higher voltage. 3.8V seems like a safe number. You want them all MATCHED at the same voltage. That's my definition of "take a charge". If the voltage is lower, there's higher risk that charging them will start a fire. I've recharged cells at low current from less than one volt, but I never left it unattended.

Whether you've managed to recharge existing cells or replaced them, you face the electronics problem.

The battery chip may have lost power. Its response varies. I never got any thinkpad chip to let me restart the battery. I managed to restart one NiCd battery that had a PIC processor by resetting the PIC. Dell C-series batteries come back, but when you press the test button, you get a flashing light pattern. The laptop battery light flashes continuously...but they seem to work ok.

Another wrinkle is that the battery remembers its current capacity. If you replace the cells, it's likely that the memory contains the old number and may not let you have more than that capacity. There are ways to reset that, but it's a secret closely guarded by the battery rebuild people.

If I'd spent all the time I spent working on this issue working at the corner burger joint at minimum wage, I could have easily purchased new batteries for every laptop I've ever owned and still be money ahead.

Are we having fun yet?

Reply to
mike

Sorry, flat == 0.00volts. To be more explicit, each cell shows 0.00 volts. "Flat".

And, of course, they *won't* take a charge in that condition!

Taking things apart to learn stuff is *fun*.

I wasn't able to see anything on each cell. Some shared electronics to which everything attaches. Plus a couple of temperature sensors (?) sitting atop a couple of the cells.

My definition is "the pack won't even try to push current into the cells" :>

I'm more interested in *replacing* as (to me) they are obviously long past the point of no return.

I didn't notice what was on the board in the battery. I'll be more observant next time I open one up.

Ah, good point!

Then, I guess it depends on what that "number" happens to be!

If you measure happiness with money, that may well be the case!

Actually, yes! :>

"A dollar picked up in the road is more satisfaction to you than the ninety-and-nine which you had to work for..." --Twain

I'll see if I have any salvaged 18650's and tie them in with some clipleads and see if the pack shows any signs of life, if the tablet recognizes it, etc. Costs nothing to try! And, based on those results, see what sorts of cells are available in that form factor.

Thanks!

Reply to
Don Y

The pressure sensor is inside the positive terminal Some shared electronics

There's several places in the "pack" where the charge can be interrupted. You have to try to stuff current directly into the cell. If the cell won't take any current at all, it's likely popped the pressure sensor.

Probably a charge control fet, a discharge control fet a processor chip various sensor taps on each cell that may or may not go directly to the processor, temperature sensor thermistor, thermal fuse, some means of talking to the computer probably I2C clock and data.

There's a windows program called PCWizard that can talk to the internal pack and tell you what the number is. But it may fail to communicate if the pack is completely dead and won't power the comm interface.

The wording of the original post suggests that these might be batteries that are added in addition to the internal pack. PCWizard probably can't talk to those...and much of what I've said might not apply.

Or you could measure happiness with the free time you get from using that money to save time and frustration charging batteries...all the while consuming delicious burgers and learning Spanish.

Maybe for half a minute. When it comes time to pay the mortgage, I'll take the ninety-and-nine.

Reply to
mike

FWIW, I rebuilt a pack in an instrument that used 18650s. Of course I bought them new and had them electro-welded. I'm not all that keen on spending time and energy with salvaged batteries. You have a task to do, you buy the parts, fix it, and get on with business.

I will repeat the other persons post about not soldering to batteries. In the words of Grand Master Flash, "Don't Do It!"

Reply to
miso

Salaged batteries can be perfectly usable -- depending on the device into which you install them!

E.g., I pulled an 18650 out of a discarded battery pack taking care to keep the long "tabs" that had been welded onto the cell to connect it to it's neighboring cells. These were ideal to connect to in the single cell GPS unit to which I installed it! If *that* cell ever dies, I would gladly repeat the exercise -- since buying a new cell would necessitate paying someone to weld tabs onto it!

Reply to
Don Y

Well...yes, but that's not what you asked about. A GPS is a much less demanding application. One cell is MUCH easier to manage. Low current evokes fewer problems with cell ESR.

If *that*

Yep, my DIY tab welder helps a lot.

You can buy cells with tabs welded on. I found that, in many laptop battery cases, they cut the plastic so close that there's not enough room to overlap two tabs and solder them.

Reply to
mike

Hi Mike,

OK. Assuming the sensor *opens* the circuit to the battery (and doesn't self-reset), that would account for seeing 0.00V on *each* cell (I can drag out a better DVM to verify it really has "zero potential").

But, what are the odds of all 8 cells (4 batteries in each battery pack) having *that* same problem at the same time?

(I can check the other battery packs to see what their symptoms are. I suspect they have just "run flat" over time)

I hesitate with the cells *all* claiming to be (completely) flat. If there was signs of life on one or more, I might try to coax them back to life...

Again: *all* of them? (and, possibly, all in the other battery packs, as well? Design flaw?)

That sounds about right. I'll drag out the stereoscope and take a closer look (my eyes are too old, otherwise :> )

Correct. These are "extended battery packs" or "expansion battery packs" or somesuch. I.e., the tablets operate off a standard battery but capacity can be augmented by attaching one of these (very different form factor, etc.)

I measure happiness by how many new things I learn and how challenging obtaining that information happens to be! Tonight, I learned how the brain processes "pleasurable experiences". (someday, I may actually *understand* what I've learned! :> )

Learning another language at my age would be WAY too frustrating and of very little reward. ("Gee, if we were to hire some latinos I could speak to them in their native tongue!" "Yes, or you could try English!")

And burgers have been losing their appeal for many years, now.

I guess it depends on whether you *have* a mortgage, or not!

I actually found the quote rather insightful. Its amusing to consider how something as "insignificant" can bring a disproportionate amount of pleasure!

I'll open the battery packs -- a couple of them so I can verify the symptoms of each -- tomorrow or next week and see what else turns up. I suspect I will have to coax the cells out of the case (double-sided tape) so I can really see what's up...

Reply to
Don Y

I won't bother trying to rebuild a laptop battery. Easier to just run them off AC. There's already lots of cruft that accompanies the laptop (well, at least *my* laptops) like power supply, power cord, network cable, USB cable, minihub, WiFi sniffer, etc. So, carrying the power adapter doesn't seriously impact the amount of bulk you're dragging along with it.

OTOH, the tablets are much smaller and can benefit from

*not* needing any of that cruft. But, then you rely on the battery, more!

If push comes to shove and the "normal" expansion battery interface won't accommodate my repairs, I can always tether the battery to the "DC inlet" that the power adapter normally feeds.

Reply to
Don Y

Instead of a pressure sensor, let's call it a non-resettable circuit breaker actuated by internal cell pressure.

That was my reaction too. I've got packs where the breaker in every cell was tripped. Only explanation I can come up with is that the cells overheat and there's some delay before the pressure builds to the trip point.

Measuring the cell voltage is inconclusive. If the voltage is zero, you could put your meter on diode test to see if they're open or really zero. I use a current-limited power supply for the test.

Yep, I've seen 'em all tripped.

I was thinking more about latinas. "Yes, or you could try English!")

That tape can be really tough. Try to bend the case and not the battery. I've punctured cells trying to get 'em out.

Reply to
mike

OK. "Vent"

Hmmm... OK, I'll buy that. Sort of like a tea kettle "whistling" after being removed from the heat (if timed *just right*)

I'll try that.

OK. I'll check the first battery pack before opening up any of the others (less risk of cosmetic damage to *all* if I just concentrate on one.)

Ah! My other half would frown on that sort of motivation! :>

Women tend to have pretty strong feelings on these things... (go figure!)

Yes. When I initially tried to remove one, I grew alarmed at how much stress I was putting on the cell. The fact that the cells are soft-sided and so "thin" and "wide" makes them even more susceptible to mechanical abuse.

(each is about the size/shape of the original iPod and perhaps

1/8" thick -- yet, covered with double-sided tape on the one side!)

If the cells are toast (you haven't claimed the "pressure vent" is resettable!), then I'm not worried about their "value", rather, any paste getting out!

Reply to
Don Y

Ok, I see where this discussion has gone horribly astray. I got fixated on your mention of 18650's and have been talking about that. And it seems that "flat" applied to the cell geometry as well as their charge level. AFAIK, the 18650, used in the majority of laptops, has a pressure switch under the positive terminal that opens when some target pressure is reached. The purpose is to prevent venting and thermal runaway. I'm sure there is a vent, but it's probably at much higher pressure. I've never found any sign of venting debris around a cell that was open-circuit.

If you have flexible cells that look like plastic baggies, there's no way to contain pressure. All my experience was with single-cell PDA batteries. The safety problem is much simpler with one cell. I've replaced them without incident. Just have to cut the plastic at the end and take out the little board and put it on the new cell.

I have seen PDA cells swell up to the point that you can't get the case back together.

It's not clear how your cells are connected. Five is an odd number that suggests they all have to be in series. That voltage is too high. If it's four cells, the logical connection is two cells tall and two wide. I'd expect they'd need the same type of balance protection that is used in laptop batteries. But I have zero experience there.

More confusion. I've punctured metal 18650's trying to get them off the tape. They're certainly not intended to come out. Soft-sided cells are considerably more delicate. I've never tried to re-use one I've pulled out of a pack. That makes it difficult to scavenge cells from other packs.

People claim to have reset the pressure switch on 18650's by stuffing a tool thru the hole in the positive terminal. I gave it a try, but was unsuccessful at pressures I was willing to exert. There's risk of puncturing the top of the cell. Even if it works, you might be left with a cell shorted by your tool and risk of explosion. Not worth the risk.

then I'm not worried about their "value",

I guess the key is whether they're individually protected or go to some common protection scheme.

Measure right at where the protected cell attaches to the product and again between the protection and the terminals coming out of the cell... depending on the configuration.

You've got to determine where the protection is.

Reply to
mike

Sorry, my fault. I mentioned 18650's in the context of (temporarily) wiring in four of them to replace the existing cells (based solely on cell voltage, nothing mechanical) to test if the "number" that the battery pack "remembers"/reports is likely to give me a useful battery pack in the future *if* I can successfully replace the "dead" cells with functional ones "having the correct mechanical characteristics"

Ah, OK. So the switch *responds* to pressure *before* the cell would otherwise vent or rupture...

These aren't as "soft" as some of the cells that I've seen but they are nowhere near as "rigid" as an 18650. I.e., I suspect if I "poked" one with my finger, I could easily deform/short it (?)

These individually tie in to a "set of conductors" (flex circuit) that runs between them. Not abutting end-to-end as is common in laptop battery packs. I.e., if replacement cells had similar length tabs (~1/2 - 1") it would be a lead-pipe cinch to replace them!

Five was a misremembered figure. There are a total of eight cells in the "battery". It appears they are arranged as four groups of two (14.8V). But, I can't say for sure if each set of two are *directly* connected together (which is what it appears, superficially) or if there is another "layer" in the flex circuit that allows each cell to connect to the "controller board" independently.

I.e., it appears that there are only *8* connections to the controller board (4 x 2). Removing the board is tough as the flex circuit ties it to all of the cells and effectively acts as a mechanical restraint holding the board in place.

I will open it up and gently poke around the individual cells. I can't tell if there are two or *three* conductors coming off each as teh connections to the flex circuit are difficult to follow without disturbing things.

Oh, OK. Yes, 18650's are more massive and tend to have less surface area so the tape seems to be more agressive. These are much larger (probably 6 sq inches on a side) so the adhesive needn't be as tough. But, there's a lot *more* of it! Sort of like having a square foot of velcro proves to be a daunting task to separate while a little piece pulls apart easily.

I'm not averse to buying new cells -- assuming they are available, affordable and *needed*. OTOH, I don't want to make a *career* out of this...

So, would you expect a similar sort of "switch" in these flat, soft-sided cells? Or, is that meaningless -- because it would be difficult to direct the pressure to a relief point? (i.e., 18650's are confined in a rigid case, these aren't)

OK. I'll get a bit more aggressive in my probing...

Reply to
Don Y

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