More capacity than I thought?

[steveho]

Just for fun, I decided to deep cycle my battery. I unplugged the a/c and checked to see that the battery was "fully charged" at 100%, and something like 8.5 Wh. The battery mizer gauge estimated about 20 minutes of runtime. I shut off all standby timers, and set the computer to maximum performance. Then I loaded up Windows Media Player and just played videos until it shutdown. Things went smooth for the first 20 minutes with the power draining evenly. After about 20 minutes, the battery light started blinking and the battery level jumped from about 50% to 4%. At this point, if I had the alerts on, the computer would have hibernated.

We chugged along... for another 40 minutes! What's going on? During these 40 minutes, it showed 0.21Wh left, running at a level of 28 watts (media player). That calculates out to less than 1 minutes, which is what battery mizer was reporting. After about 30 minutes of this, the Wh level dropped to 0, and I was still drawing about 28 watts. That went on for about 10 more minutes until the computer just turned itself off (battery voltage dropped to less than 9.5).

My question is this: Is there a way to reset the Wh remaining? Or the battery itself? It seems like the battery is reporting incorrectly. The computer shouldn't shut itself off at 20 minutes, when there are 40 more minutes left...

Anyone know what's up?

[RoundSparrow]

I think what you describe is part of the reason you are supposed to deep cycle

What is the cycle count on your battery?

[lfeagan]

For starters, search the forums. I think you will find a simple query would have led to useful results.

Anyways, these are Li+ batteries, not NiMH or NiCD.

This is a great website for info:
http://www.batteryuniversity.com/

Among other things they say:

If possible, do not discharge lithium-based batteries too deeply. Instead, recharge more often. Allow a nickel-cadmium battery to fully discharge once every 30 cycles or so. This also applies to nickel-metal-hydride but to a lesser extent. Exact data as to how often a nickel-based battery should be discharged is not available. Neither do we know low long a lithium-ion will last under different depth-of-discharge regimes. Manufacturers typically specify lithium-ion at an 80% depth-of-discharge.

So, as for the weirdness with the timing information, the implication there is that you need to recalibrate your battery. Try doing the "recondition battery" which can be found under the "improve battery health" menu on the battery information button/icon.

[DrSmile]

Isn't the reconditioning method IBM describes the same thing as a deep discharge?

I have never had good success trying to deep cycle the Li battery, it never gains back any watts. I also have noticed that my laptop runs for another 20 or so minutes once the gauge reads zero, even with a battery that has only a few charge cycles on it.

So I would also be interested on how to reset the battery wattage if this is at all possible. I'm sure there must be a hack way (without blowing yourself up)!

[lfeagan]

FMI on the SMBus within the cells I suggest reading this. BTW, this is the device that is reporting incorrect capacities. So, reading about it might be a really fine idea as it is what you would need to reprogram to fix it.

http://www.batteryuniversity.com/partone-17.htm

[krosenstein]

So the SMBus is necessary to monitor battery performance?