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I'm using an HP Mini 2140 with Ubuntu 12.04 installed on it. Two months ago, due to the fact that my old battery lasted only for about 20-30 minutes, I bought a new battery, which reported a capacity of 50+ Wh after charging it overnight and starting up (If I recall correctly, it was 56,5 Wh) and lasted for about 6 1/2 hours at most.

During those 2 months, when checking the battery capacity with gnome-power-statistics (and acpi -i), I found out that after some charges, the battery capacity dropped significantly to ~48 Wh at some point. I started investigating the issue using Google and read about battery calibration. I attempted to calibrate the battery by doing a full charge, full discharge and a full recharge. The battery still reported the same capacity; however, I noticed that even after the battery had reached 0%, it would still power my netbook for a significant amount of time.

Some time later, the capacity dropped until it stabilized to 42 Wh for about a month. One week ago, I noticed that it dropped to 38 Wh and yesterday it dropped to 33 Wh. I attempted to recalibrate the battery and found out that my battery reached 0% after 4 hours and lasted 2 more hours until my netbook powered off, which means that the battery hasn't experienced any significant drop in capacity.

I also stumbled upon this article, which makes me suspect that the issue has to do with ACPI.

Is there something I can do to fix or work around that issue? The only workaround I've come up with is to disable suspend/hibernate on low battery. The BIOS does not seem to have any feature to calibrate he battery and it doesn't seem possible to perform any sort of reset on the battery or ACPI.

EDIT: I'm using a non-original battery.

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The ACPI implementation is made by the manufacturer (HP), so unless you find a BIOS update for your model, there is no way to fix this.

But for clarification: it is never possible to exactly determine the battery capacity (and with it, it's wear). Everything about Li-Ion battery capacity is better or worse guesswork. The battery calibration which you have done is basically a way of letting the battery run down from full to empty to see how much energy can be extracted - it needs to be done that way because there is no other way of determining the capacity.

Since you report that the battery lasts even after the percentage has dropped to 0% (which is again just a guesswork), your real capacity is well over the value stated by the ACPI system (and displayed to you by the gnome-power-statistics), so your actual wear is not as bad as it seems.

Also, often non-genuine (3rd party) batteries often show a different behaviour from original manufacturer batteries, so that might fool the ACPI implementation into guessing the wrong values.

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Possible things to check:

  • Manufacturer's website for any recalls
  • Firmware updates to the battery
  • BIOS firmware updates
  • See if the battery capacity reported is the same on Windows as it is on Linux to rule out the OS (I know, ugh, installing Windows or using a USB drive)

In my experience, the battery firmware usually reports these numbers, a very small microchip in the battery is what determines the charge level. So it could be that that is malfunctioning, or a firmware update might fix it... hard to say.

If you can update anything mentioned above, avail yourself of the chance to try it, but otherwise I'd hold off until/unless someone with specific experience with this laptop chimes in.

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I'm using a 3rd party battery, so 1 and 2 don't apply to me. In addition, all BIOS updates for my netbook don't make any references about the battery or the ACPI. I also don't think it has to do with the OS due to the fact that if I discharge the battery to the "virtual" 0%, shutdown and try to power on my netbook, it will not start up and the battery LED will start flashing. – Alexandros Sep 15 '12 at 11:06

The cause of the problem cannot be software, since you say it worked just fine for two months. The problem must be a hardware defect in your battery that caused its performance to degrade significantly.

As this is a new laptop, use the warranty and demand that the battery be replaced. If this happens again, demand the replacement of the laptop.

You should be aware of the fact that all batteries degrade with time and must be replaced every few years, depending on the quality of the battery, its use and the ambient temperature. Heat extremes will especially shorten its life-time, so I should check if the laptop overheats and take steps if necessary. But two months is still much too short.

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Still, the fact that I can get 2 hours of battery life even when the battery has dropped to 0% cannot be explained by the fact that my battery has degraded significantly. – Alexandros Sep 14 '12 at 18:38
Battery life may not be the problem here, but calibration. We don't know what has changed, so trying another battery may clear up some of the mystery. But before that you should try (1) The Battery Test diagnostic available in the boot F2 System Diagnostics, (2) Recalibration by fully charging/discharging/recharging as is detailed here, (3) The maintenance advice from here. Some other useful advice is here. – harrymc Sep 14 '12 at 19:09

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