Problems with refurbishing a laptop battery pack

Agro · 2018-11-20T16:31:32.000Z

Some time ago I started a task: replace cells in my fiancée’s laptop. It was a 6-cell one, 1 row of 2 cells and another of 4.
Encouraged by videos, I read some tutorials, bought a set of 35E.
Got real troubles soldering to cells but I have that sorted out, mostly thanks to a better iron and better skills.
Soldered it together…the 4-cell row doesn’t fit. By far.
See…my connections were much thicker than the factory ones.
Ripped most of joints, left just the 2 thinnest ones. Cleaned the battery ends, tried to put it together before soldering new wires.
Doesn’t fit, by far.
The case had some hair-thin vertical fins, seemingly too small for stiffening. Removed them, that didn’t really help.
Ripped the thicker joint, shaved the thinner one with a knife so it was now really as thin as I can do.
Fits, but I needed to force it together. And I still had only 1 joint.

Something’s seriously wrong….I measured the cells.
My 35E are on average 65.25 mm. The original cells are on average 64.85 mm. So I lost ~1.6 mm by using different cells and further space by thicker connections. I find it very surprising that the factory decided to make it so tight.

I checked my other cells thinking that maybe I could replace the 35E (or at least some of them) with something shorter. Nothing reasonable. And I have no budget to buy different cells.

I needed to get creative….I took a closer look at the case. The case had 4 grooves to support it in the laptop, 2 on the 4-battery sides and another 2 on the 2-battery sides.
If I removed one of them and closed the opening with epoxy; then removed the corresponding part on the laptop case; then glued the battery to the laptop case with a reworkable glue (silicone f.e.) I would lose some strength, but it should be good enough nevertheless.
I cut off the plastic around the groove, so a cell sits in its place.
Now it fits easily, I have maybe 2 mm of free space.
But that’s just not enough with my 26AWG stranded wire and my skills, I just won’t be able to do the missing connectors and still have it fit.

I have one idea for further space savings, but I’m scared of it and the benefit ain’t great. Thin-down the negative cell terminals with a file a bit, maybe that will save me another 0.2 mm, 0.05 per cell?

My fiancée is battery-less now and really frustrated because the power adapter connection is unreliable. I need to find some solution.
Any suggestions?

ChrisGarrett · 2018-11-20T17:37:31.000Z

I’ve taken two Sony VAIO packs apart and one HP, scavenging the cells.

The problem apart from fitment and getting things soldered properly, is dealing with the BMS (battery management system) circuit and whether it’s been shut down for good, if the pack stopped working. Sometimes the circuit can be reset, but often times once it shuts down due to a weak cell, or string, it’s done and adding fresh cells won’t reset things. This is similar to tool battery packs and the thermistor. You need to do both, but laptop packs have a BMS circuit located in the pack and you’re not going to replace that if it’s bad.

I was just given my sister’s minty 2012 Dell Inspiron without a power supply and with a non-working battery. I started looking at battery packs—OEM Dells before the power supply arrived and they were only $36-$42 shipped.

I don’t know where you live, so getting stuff like that might be problematic, but you’re right, the manufactures shoe-horn those cells in pretty tight and while I’m pretty handy, I don’t know if I could have done a one-for-one swap. Also, I pretty much destroyed the plastic cases with my Dremel tool, getting the cells out, so that alone, was going to be a non-starter.

Good luck, but sometimes it’s just easier to pony up the scratch and buy a new one.

Chris

Agro · 2018-11-20T18:06:20.000Z

Definitely easier to buy, but I’d rather avoid the cost.
I came up with another 2 savings:

mix the 3 best of old cells (they are ~1000 mAh each) with 35E, so in each parallel pair there’s a new cell and an old one. All 3 could land in the 4-cell row saving ~1.2 mm. I’m not happy about making that change though…
straighten out the strands of the wire, laying them parallel. 0.6 mm?

ChrisGarrett · 2018-11-20T18:14:03.000Z

Agro:

Definitely easier to buy, but I’d rather avoid the cost.
I came up with another 2 savings:

mix the 3 best of old cells (they are ~1000 mAh each) with 35E, so in each parallel pair there’s a new cell and an old one. All 3 could land in the 4-cell row saving ~1.2 mm. I’m not happy about making that change though…

straighten out the strands of the wire, laying them parallel. 0.6 mm?

Man…you never want to mix cells not of the same same batch code and not of identical health, especially when running them in series, or even a series/parallel arrangement.

That’s rule #1 and you’re breaking it.

Remember, laptops do a pretty good job of banging on cells and heating them up pretty good.

Good luck.

Chris

Virisenox · 2018-11-20T18:25:17.000Z

Agro:

I find it very surprising that the factory decided to make it so tight.

The manufacturer is all about saving as much space as they can. The more compact the laptop is, the better. Of course they’d pack the cells in tight. Not to mention you wouldn’t want them to a wiggle around and wear out the connections.

They’re able to make it so tight by using thin nickel strips that they spot weld to the cells. You won’t be able to make connections that small with a soldering iron.

Agro:

mix the 3 best of old cells (they are ~1000 mAh each) with 35E, so in each parallel pair there’s a new cell and an old one. All 3 could land in the 4-cell row saving ~1.2 mm. I’m not happy about making that change though…

This is a horrible idea. This will only brick the battery worse than it’s already bricked, and it may even be a fire hazard.

kikkoman · 2018-11-20T21:48:58.000Z

ChrisGarrett:

The problem apart from fitment and getting things soldered properly, is dealing with the BMS (battery management system) circuit and whether it’s been shut down for good, if the pack stopped working. Sometimes the circuit can be reset, but often times once it shuts down due to a weak cell, or string, it’s done and adding fresh cells won’t reset things. This is similar to tool battery packs and the thermistor. You need to do both, but laptop packs have a BMS circuit located in the pack and you’re not going to replace that if it’s bad.

This.
Check the thermal fuse for continuity before you do anything. If it has been tripped, your chances of reviving the pack just by swapping cells (and bridging the fuse) are very low. (In addition to the physical fuse many BMSes have an internal error flag that shuts the pack down)

Also: some packs apparently shut down permanently when a bank of cells is removed (and reconnected) so a cell swap has to be done “hot” .
If you know the BMS chipset manufacturer and part number you MAY find out what what booby traps there are (some are poorly documented, some NOT AT ALL. Renesas for instance. It’s like these parts don’t even exist).

There’s a few businesses in eastern Europe that reset packs for a fee (I know of several in the Ukraine). For a hobbyist without the equipment and software, FW level “repairs” are pretty much impossible and not worth it. Even a €120 spare is cheap in comparison.

Macka17 · 2018-11-20T23:36:26.000Z

You mix ANY battery’s of differing capacity,age.
the worn ones will permanently drain the better ones.
Quick flattening. permanent, never top up Charging. etc.

We had that on yachts yrs ago with multiple battery’s in house or starter banks.

They cheap enuff on net.
My spare for Dell Lappie cost me $47 AUD del.

Some you can’t win mate.

FlashPilot · 2018-11-20T23:56:45.000Z

Argo, you are well on your way to potentially blowing yourself up and/or creating an extremely hot lithium fire that will be nearly impossible to extinguish. Also, overheated cells dont even have to combust to venting large amounts of toxic fumes. Warnings are everywhere online (and probably on the sticker you just ignored on the pack), so this should mostly be common sense.

As ChrisGarrett eluded, NEVER mix cells in serial configuration that are not matched from the same batch (mfgr, model, date code, resting voltage). And if used previously, they should all be properly tested to verify they remain close in resistance and capacity and have all been used concurrently. Many reputable manufacturers test cycle brand new unused cells before putting them into service as part of their QC requirements. Injuring yourself from your own incompetence and the shitty advice and practices of others is one thing, and you have now been warned. Injuring someone else is a whole other level of stupidity you risk inflicting upon someone else. So please, just don’t do it.

You’ve also added another layer of significant additional risk by heating the cells and soldering terminal/wires without the use of proper spot welding equipment and procedure designed to allow the cells to remain cool while tabs/buttons are electronically spot welded to them. And it sounds like you’ve heated them more than once, which pressed your luck even further. At this point, PLEASE do yourself and your GF a HUGE favor and buy a new pack. The cells you just soldered should now be completely discharged and discarded. Just because others assume the risk and post articles online of their dangerous practices does not make it any less dangerous or foolish. Furthermore, even if you bought new cells with spot welded tabs installed, and were able to circumvent/reset the BMS, you still have no idea what tolerances the spec was designed for and how your mod might impact all the variables you just introduced. All packs are different, which is why reputable certified insured companies that rebuild them typically do so only with the ones they thoroughly understand and have experience with.

Yes, it sucks to waste so much effort tearing into a stubborn pack while investing hours attempting the rebuild. A few extra hours at work might easily have paid for a new pack or 2 and put you far ahead of the game. But you may very well have just saved your ass and those around you by walking away now. Ive learned plenty of lessons through life the hard way and am always glad to dispose of a ticking time bomb when someone more knowledgeable points out my errors. Your losses now are less than dinner for two, assuming you dont take her to McDonalds or pizza. Best of luck to you, friend!

Agro · 2018-11-21T09:11:03.000Z

You talked me out of the cell mixing. Thank you all.

But I’m not giving up yet.
I’ll try with just flattened wires next.
I think it won’t work….but maybe.

For the next step……what if I just turn it to 3s1p? Capacity will suck, but at least it should work. I’m a bit afraid of overloading the cells, but 35E aren’t bad. I will measure the old cells’ IR. I fully expect it to be more than double that of 35E, but I need some further margin to account for 35E wear. If I don’t have that margin…I won’t do this.

I’d really try to do w/out buying a new pack as my budget until Q3 2019 is extremely tight.

Lexel · 2018-11-21T15:33:27.000Z

Did you try to buy those 0.15-0.25mm copper sheets used for heat sinks or so?

Cut them in 10mm wide strips and solder to the batteies

100x100x0.2mm below 1.5$ shipped
https://de.aliexpress.com/item/99-9-hohe-Reinheit-Kupfer-Blatt-Cu-Metall-Flache-Folie-0-2mm-Dicke-Reinem-Kupfer-Platte/32882328573.html

When soldered then use a cutter knife and sand paper to remove the solder on the exposed side

Agro · 2018-11-22T11:00:33.000Z

Thanks Lexel.
Frankly, I’ve been thinking about tabs before as well.
The original ones are 0.2 mm.
I have some 0.2 mm 15x15 mm shims on the way, might be too small for that. I didn’t know there were larger sheets available as well, I must get one some day.
But I don’t really want to wait….at this time of the year I expect that a package would take 2 months to get here.

I decided to try flattening the wires and just that.
If that doesn’t work, I’ll go with just 3 cells. 35E should work, but if they don’t - I have some HG2 that I could use instead; they’ll surely have the IR that I need.