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I just noticed a few days ago that Windows 7 hardly refreshes the battery charge (or current capacity, expressed in percentage) as the battery is discharging or charging. I had it jump from 100% to 80% then to 20%; today it really bit me as it jumped directly from 96% to 0% - as in Windows didn't even had the chance to notice the battery was almost dead, so the laptop ran out of power (I forgot to plug it in to AC).

What is the problem here? The BIOS has no option even remotely about the battery and the diagnostic options only have memory and HDD tests; the log is totally empty. I'll give HP a call, but I'm not looking forward to it, as the customer service is horrible, at least in my country.

The laptop is a HP Pavilion dv5-1101en.

Edit: It's currently charging and it did something similar: the charge jumped from 2% to 7%, then it started increasing steadily as one would expect.

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CPUID Hardware Monitor also reports the same charge as Windows, so I suspect Windows isn't the culprit here. – Mircea Chirea Aug 24 '10 at 13:09

4 Answers

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Your battery is probably just not calibrated right. The battery after a lot of usage forgets what is 100% and what is 0%. What you want to use is to charge the battery until it's full and then keep it plugged in for a couple of hours to establish 100%, then disable the critical and low battery functions until the battery dies to establish 0%. Then recharge.

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Right, this is what I did - although without knowing it. So I guess it's all fine now. – Mircea Chirea Aug 24 '10 at 21:17
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My old HP Compaq nx6325 was doing the same thing. I used this tool from hp to test the battery. This tool shows you if your battery is ok, defect or needs to be replaced soon. Mine failed... but, after replacement, everything is working as expected. There is also a site from hp if you have problems with your battery.

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How old is the laptop? As the battery ages the available runtime lessens but also the reported value becomes less accurate to the point where my old laptop always registers as 0% charged.

If the battery is relatively new (i.e. < 1yr) then it could be a faulty charging circuit causing the odd readout.

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The laptop is about 1 year and a half old, but it has been sporadically used, much less on battery. HWMonitor says the wear level is 15%. – Mircea Chirea Aug 24 '10 at 14:30
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I use the free BatteryBar utility instead of Windows own battery indicator, which I first found through Gizmo's Freeware, and posted about on my blog Steve's BPCA Blog back in April 2010.

I find it works well for me and gives me better information.

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