Bad laptop battery - repair/replace/replace cells?

Thread Starter

strantor

Joined Oct 3, 2010
5,324
Laptop battery BT04XL for HP Folio 9480m, Laptop says 0% plugged in, not charging. This is following a 2yr timeout for bad behavior in the bottom drawer of my desk, and then reinstall of Windows 7. IIRC it used to work.

I thought maybe it was just the drivers for the battery charging since I installed new OS. Uninstalled, reinstalled, updated drivers, etc. no change. Opened up the battery and measured each 3.7V cell: 2.5V, 2.8V, 1.4V, 2.2V.

I thought maybe the voltage was just too low for the laptop to start charging, so I attached my bench supply to the pack and charged it for a couple minutes at 1.5A. Got the pack voltage up to almost 15V.

Put the battery back in the laptop, now it says "1%, plugged in, not charging."

I'm guessing it's hesitant about charging the unevenly balanced pack. So if I disassemble the pack and charge each cell individually and put it back together, what are the chances of that working? I mean are they really "bad" or are they just unhappy about sitting for 2 years? I'll probably try it this weekend; just want to know it will be a waste of time.
 

dl324

Joined Mar 30, 2015
11,317
I have a laptop with a battery that's seen better days. Wouldn't even consider trying to replace cells even if it was possible. When manufacturers assemble packs, they start out with matched batteries to get the best performance and lifetime.

Even if you replaced all cells, you aren't likely to have the equipment to verify that you have good cell matching.

If a replacement battery pack is a significant portion of the price of a new laptop; time for a new laptop. Or just treat it like a corded appliance.
 

SLK001

Joined Nov 29, 2011
1,548
Try to individually charge each cell to 3.7V and see if it comes out of its stupor. If one or more cell can't reach 3.7V, then you have found your problem. The charger should monitor each cell to verify that it is charging properly.

If you decide to replace the cells, do you have a spot welder to attach the metal strips to the cells? Without one, I wouldn't even try - if you solder the connections, you'll have to shoe-horn the cells back into the case.

Have you priced the cost of a generic replacement pack?
 

Thread Starter

strantor

Joined Oct 3, 2010
5,324
Currently charging individual cells without disassembling the pack. Very carefully dug through some epoxy and silicone to access the tabs soldered to the bottom of the PCB and found a way to finagle some DMM pincer clips down around the lower tabs, and connected the power supply leads to the DMM leads. Seems to be working.

20180428_093551.jpg
 

ian field

Joined Oct 27, 2012
6,539
My money is on “waste of time” but if you’ve got the equipment and patience, seems worth a shot.
Some makes use a whole life "fuel gauge" non volatile chip - IMO: that sometimes declares the pack "dead" when there's plenty of life left in the cells. Without the means to re programme such a chip - it might be an exercise in futility.
 

wayneh

Joined Sep 9, 2010
16,399
Some makes use a whole life "fuel gauge" non volatile chip - IMO: that sometimes declares the pack "dead" when there's plenty of life left in the cells. Without the means to re programme such a chip - it might be an exercise in futility.
That's annoying. I had exactly that type of thing in cartridges for a printer. I bought a cheap resetter and was very happy
with how well that worked.
 

ian field

Joined Oct 27, 2012
6,539
That's annoying. I had exactly that type of thing in cartridges for a printer. I bought a cheap resetter and was very happy
with how well that worked.
You may have to study hacker pages for battery packs - but I haven't bothered watching the catalogues.
 

Thread Starter

strantor

Joined Oct 3, 2010
5,324
Charging cells individually didn't seem to work. Maybe if I had given it more time.... I don't know. I only charged them 10-15 minutes each at 1.5-2.5A; enough that each cell was steady above 3.7V. Laptop still says 1% not charging, and dies immediately when I unplug the A.C. adapter.

I don't know what's going on in those electronics in the battery but I'm guessing it tracks current in and current out, and since I bypassed the electronics to charge the battery, it has no way to know they batteries have more charge than before.

Anyway, I'm moving on. The laptop was a gift for my daughter and I missed my chance to fix it before her birthday.
 

ScottWang

Joined Aug 23, 2012
6,926
You can try to charge the battery use 10 mA low current and when the voltage up to 3.2V then stop to charge, and charge it with the normal charger.

LM317 10mA constant current → Relay N.C contacts → Battery (+) → Vin(+) LM393 → LM393 Vout → Rb, npn bjt(or N mosfet) → Relay Coil.

LM393 3.2V comparator -- when the battery voltage reach to 3.2V then the Vout of comparator become low to turn off the bjt or N MOSFET and also turn off the relay coil and then the contacts become open and stop to charge the battery.

You can use the voltage meter to measure the battery before you charge it and after 1 hour later when the battery start to charge, if the voltage there is no any increasing then the battery could be damaged.
 

MisterBill2

Joined Jan 23, 2018
6,757
You can try to charge the battery use 10 mA low current and when the voltage up to 3.2V then stop to charge, and charge it with the normal charger.

LM317 10mA constant current → Relay N.C contacts → Battery (+) → Vin(+) LM393 → LM393 Vout → Rb, npn bjt(or N mosfet) → Relay Coil.

LM393 3.2V comparator -- when the battery voltage reach to 3.2V then the Vout of comparator become low to turn off the bjt or N MOSFET and also turn off the relay coil and then the contacts become open and stop to charge the battery.

You can use the voltage meter to measure the battery before you charge it and after 1 hour later when the battery start to charge, if the voltage there is no any increasing then the battery could be damaged.
That sounds reasonable. I can set the current limiter on the charger to 10mA and then set the voltage to 3.2 volts. Now all that I need to do is to open the battery pack case without destroying it. THAT will be the really challenging part.
 
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