This is really calibrating the measuring system. Is that correct? I've heard about this, but never had it explained clearly.
Some systems that I have list battery capacity as percent remaining. Others list it as time remaining. The challenge with using time as the measuring stick is, of course, that it's dependent upon the specific load.
I've seen some systems that appear to base the time left on the instantaneous load. If I turn up the brightness on the backlight, time left will drop and turning down the backlight does the opposite. Other devices seem to attempt to base the time left on the average consumption from full charge. It would be nice if all the systems were consistent.
The funny thing is that this really isn't a new problem. Every car I've owned has had a different accuracy curve for the gas gauge. It will move slowly for the first half of the gauge, then drop quite fast once indicating below half a tank. The gage does nothing to compensate for the difference in fuel consumption in the city vs. on the highway.
I understand that the car gage is simply attempting to display the quantity, not rage. Eventually, I get an internal sense for range. I kind of do the same with my electronic devices. I calibrate my head.
Duane -- I really don't find either of the display systems more common than the other. The gas gauge is a coulomb integrator. Good ones also monitor the terminal voltage, and in this way can also tell when a battery is unserviceable. The game can be played that at the current rate the battery has this much left. Personally, I prefer the % capacity meter instead of time -- but this is because I have to deal with the non-linear battery (think of adding water to the flodded lead-acid cells during charging, to throw a kink in the total charge calibration, for example). We humans like to think of the world as balanced: if we take out half of the amount of charge from the battery when we start fresh, then put back the half we took out, then we want to be back at full charge again. But this doesn't give an accurate picture. Therefore, I will cover gas guages in a future post. That's cooking with gas!
Duane: the calibration is for the measuring system, yes. It has to compensate for the fact that our world changes, and not for the better (be thinking -- entropy and such other random thoughts). Just a very very little piece of humor, there. But really, if everything always behaved in a well known/predictable manor, re-calibrating would not be needed.
My good buddy in high school showed be why the car gas gauge is so non-linear -- when you look at the shape of the tank, it is rectangular (vertical walls) at the top, and then slopes at the bottom. A gauge that floats on top, is going to move faster at the bottom...simple as that. The simple fix for that is just to make the 'tick marks' for the remaining fuel be non-linear on the meter as well. Voilla.
> Laptops and their batteries seem to be some of the worst offenders...
My work laptop - a Lenovo T510 which is showing its age in other respects - has a great battery with over 3 hrs life BUT best of all the run time indicator is almost bang on. It is in time (hrs/min) which I reckon is the most useful indication (which answers Duane's question) but switches to % when it is on charge. I have never recalibrated it and it's only a couple of minutes out -if that - at the end of the battery life. I guess I am lucky....
Are the ubiquitous computer memory "coin cells" - 2032 et al - Silver oxide or another chemistry? They are nominally 3V so if Silver Oxide they'd have to be 2 cells in series so I suspect they are something else?
The 2032 and similar 3V coin cells are a non-rechargable Lithuim chemistry. I used to know what one but can't remember the details right now. I guess we'll have to wait for a future article from Ivan...
David: yep, pics of batteries would be nice. I tend to shy away from showing one, for fear that someone take issue that the one I picked was a lousy non-representative sample, or some such. For the truely bizarre technologies, I will provide a pic or two, however.
Even from the big boys like Varta and Tadiran who make Lithium Thionyl Chloride coin cells, they are primary batteries. When used for memory backup on a computer motherboard, for example, a small leakage current is allowed back into the battery, which makes the battery last a bit longer than it would without the current. However, it doesn't 'recharge' it in the conventional sense. Have you found a manufacturer that claims to have one that is rechargeable? Are you sure it is Li-SOCl2 chemistry? You can see from my part-7 post in the series, these are in the energy-density range to be primary batteries.