How do they measure "battery life"?

[miamirice]

When the specs about a notebook refer to the "battery run time" what kind of usage and power setting do they use to make this estimation? LCD brightness at the lowest setting (zero bars), no ethernet and playing Minesweeper while sitting in a refridgerator?

I just got a T42 and after going on battery this weekend I was cut pretty short of my expectations. The specs say 3.8 hours, but I got like 2.5.

[davidspalding]

Try using the Power Manager schemes (double click that battery thingie on the taskbar). And have it display in time remaining, not %. One called Power Optimized, or the Max Battery Life, should give you more then 2.5 hours.

Also, when I was looking through that utility, there was a "battery conditioning" function from teh last tab, that adjusts the metering mechanism to be more accurate. You need to leave it plugged in for several hours, as it charges the batt, discharges it, then charges it up again. I've done that to both of mine, and the PM "time remaining" gauge has been the most accurate I've ever seen.

[christopher_wolf]

Does the T42 have the same Power Manager as the T43? I thought it either wasn't there or it was very different.

[miamirice]

Hmm...the T42 does have the power management setting as a part of the "Power Settings" and all that. I don't know if it's the same as the T43, but there are at least two to choose from. There's also some utility on the Thinkpad which I can't remember now - I don't have the notebook on me - which is supposed to help with that. And yeah, I'm rather fascinated with the battery conditioning thing, which I have yet to try out.

In any case, I'm still wondering *how* is battery life calculated? If it assumes things like no wireless or ethernet and dimmest settings...while it might keep you going long...how reasonable is it to expect such low-level usage? It's like the MPG ratings and those hybrid cars...none of them actually perform that way.

[davidspalding]

If you Google for some LiIon battery technology white papers, you may find some interesting reading. If memory serves, one of Li Ion's great benefits over NiMH was that circuitry could be developed to more accurately measure battery consumption rate. By knowing what the total power capability of a battery is, and measuring drain, yada yada yada. I don't have any handy links, but I'm sure you can scare some up.

Here's an interesting one I found by accident. Doesn't answer your question -- I think -- but related directly to Thinkpads.

http://www.cs.huji.ac.il/course/2004/po ... mation.pdf

[madmatrix]

Very interesting test. I think the good 6-cell battery generally can last more than 3 hours with Thinkpad default power scheme.

[christopher_wolf]

I have gotten my 9-cell to go to around 5:30 Hours when I first got it. It all depends on how you use your system; the more activity per unit time, the more, non-monotonically increasing or decreasing, the power consumption. For example, to get the maximum battery life possible on an iPod, it is recommended that you do not touch any of the buttons and let it play through a playlist at a default volume; I *highly* doubt that even the majority of people who have iPods do that. Same with a Laptop, bursts of activity really do not help the battery life estimation at all (yes, an estimation...it will not be exact) because, for the most part, the usage is unpredictable at best. The power schemes are designed to limit the variation introduced by the user clicking around on everything and starting up a bunch of processes that can ran for pretty long periods of time. Becuase of this, it is almost non-causal and, as a result, the battery gauge as some difficulty in getting the exact time .