Acer Aspire Laptop - Battery Confusion

[edpalmer42]

I've got an Acer Aspire laptop.  Yeah, I know, not the best brand.  But it's 17" and it was free!

It's been working fine for a few years, but now it seems to be confused about the battery.  I have two batteries.  One went dead while in the machine.  I had set the laptop aside and hadn't powered it up for a few months.  That battery is dust.  I tore it open and one set of cells is at 1V1. 

The other battery is fine, but the computer doesn't think it is.  If I charge it, the computer charges it to about 37% and then stops charging and starts flashing the battery light to indicate a battery fault.  If I remove the battery, I can charge it manually to 16V8 (4 cell battery) at which point, the battery disconnects as it should.  It's almost like the computer thinks the battery is 1/3 of it's actual capacity and when it keeps drawing current, the computer thinks something's wrong.  I've got a couple of battery monitoring apps that agree on all the battery parameters so it seems like the battery is reporting correctly.

I've cycled the battery, I've removed the battery and then held the power switch for 30 sec. (apparently that's supposed to clear something in the computer).  I've cleared the CMOS.  I replaced the power brick with a beefy linear supply.  I even nudged the voltage higher than the normal 19V5.  Nothing changed.

Any thoughts on how to proceed - other than a large hammer? 

Ed

[Zucca]

I suppose the battery control board  is broken.

Laptop and batteries communicate with digital interface, in this way the PC knows what battery is connected. If you feel superman take the control board of the old battery and put it in the one with good cell, or swap the cells in the old battery.

 

[edpalmer42]

I have a source for used cells so my next step will be to replace the bad cells in the bad battery.  I'll measure the capacity of all 3 cell pairs to make sure they're similar.  Hopefully, this battery isn't one of the ones that has to be kept powered at all times.

I'm also starting to suspect that the 'good' battery isn't really good at all!

Ed

[SaabFAN]

How is the charging current curve when you charge the empty battery with the linear supply?
It could be that the current drops off when the battery is at about 37% charge and the Charging-IC thinks the battery is full.
Many charging-ICs go into a trickle-charge mode when the charging-current goes below a set threshold.

[edpalmer42]

The battery with the dead cells won't charge at all.

The other battery tends to ramp the voltage up fast at the end of the charge and ramps down fast at the end of the discharge.  On charge, I tried holding the voltage just below the cutoff point to see if it needed more time to finish charging, but the % charge didn't really increase.  The fast ramps at the end of both charge and discharge have me thinking that one pair of cells in that battery is failing, too.  That would explain why charging ends prematurely.

If I can successfully replace the dead cells in the dead battery, I think the next step will be to tear apart the second battery and test those cells.

The dead battery (unknown age) was free and the other battery (3 years old) was the cheapest 8-cell battery I could buy on ebay so I'm not really upset by the current state of either battery.  This is the first time I've had any reason to repair a battery pack so it's an interesting learning exercise for me.

Ed