X201: erratic battery gauge [ Edited ]

[artami]

The battery gauge on my x201i  (Windows 7, 64 bits) seems unable to make up its mind about how much time is left on the battery. I got the thinkpad a week ago, so everything is brand new. 

Without me changing any of the settings or the apps I use it will display for instance 6:00 hours left, then 5 minutes later decide it's only 5:15, then up again to 6:15, down to 4:30... up again... Makes it useless as an estimate of how much time I have left on battery!

On one occasion just after waking it up from sleep mode it displayed 20 hours for a few minutes! And there was that time when it even said 50 hours... 

Any ideas about what to do ? 

Many thanks. 

Moderator Note: Edited subject to match content.

[artami]

PS: the issue  seems to be worse when the battery is at 40% or over. 

[79dan]

Same issue here! It's very frustrating. I already did a battery reset, but it didn't seem to help at all. Any ideas anyone?

[JNavas]

This is normal. The battery gauge shows the estimated remaining runtime based on your current actual power consumption, which (depending on your power profile) changes with system load, so the estimate will vary as your power consumption varies.

[79dan]

Yeah, thanks, that's what I read in other threads. Also, there seems to be a discrepancy between the remaining time reported by Lenovo's Power Manager and Windows (the little battery icon). I'm wondering which one will be more accurate. This is actually the first time I'm discharging the battery just to test it.

[JNavas]

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79dan wrote:

Yeah, thanks, that's what I read in other threads. Also, there seems to be a discrepancy between the remaining time reported by Lenovo's Power Manager and Windows (the little battery icon). I'm wondering which one will be more accurate. This is actually the first time I'm discharging the battery just to test it.

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FWIW, I've personally found the Lenovo Power Manager estimate (on many different ThinkPads) to be more meaningful than the Windows estimate.

UPDATE: I've run into a case of the Lenovo Battery gauge (Power Manager 3.61) being wildly inaccurate, problem that needs to be corrected by Lenovo:

[JNavas]

Short while later:

[Mark_Lenovo Administrator]

John,

Could be an individual incident - I've not seen wide reports.

Version 3.62 is out now... might be good to just update and see if either the new code or act of updating solves it.

Mark

[JNavas]

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Mark_Lenovo wrote:

Could be an individual incident - I've not seen wide reports.

Version 3.62 is out now... might be good to just update and see if either the new code or act of updating solves it.

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In addition to this thread, I have seen other reports of inaccurate Battery Meter (e.g., link).

Regardless, even rare errors should not occur unless Lenovo doesn't really care about quality --

"works most of the time" is not the standard customers expect from ThinkPad.

In my case I think it was caused by suspending the computer with a partial charge,

and the Battery Gauge then miscalculating recharge time from time spent suspended.

UPDATE: I'd be happy to try Power Manager 3.62, but it's not being offered yet by System

Update, and the download page on the Lenovo webpile is broken. Working link please.

UPDATE2: Download page now working. Thanks.

p.s. Having embedded images converted to links is quite annoying,

in part because the 50K limit on embedded images is absurdly low.

Regardless, this should be handled in your forum software,

which could check image size, and offer an option to reduce it.

[ColonelONeill]

Think of it this way, if you're mathematically minded:

P = power consumed in watt-hours.
dP/dt = instantaneous power consumption in watts

Knowing dP/dt, one can integrate to find watt-hours, and estimate total battery lifetime.

When dP/dt fluctuates based on usage, the estimated battery lifetime will fluctuate accordingly (sometimes wildly, as is the nature of the extrapolation formula).

The inaccuracy inherent in all estimates (which is why they're called estimates) varies based on the algorithm used to predict average dP/dt. Each algorithm may be good for some cases, and terribly bad in others.

In your particular case, the algorithm may be sampling the wattage (seeing as it's impossible to obtain an instanteous reading) while the system is in the process of switching to the battery and not bearing the full power draw. (Alternative explanation: sudden change in clock speed skews the sampling interval, and ends up showing the same unrealistically low wattage.) Furthermore, as it begins to accrue valid, accurate wattage sample points, it averages them out with the existing wrong value, so it takes a while for it to stabilize. (This is a fault of a moving average algorithm; but it does prevent excessive fluctuations during consistent usage.)