Does it really do that to a large degree or were you referencing something I said in the past.
It does seem to be a fairly large swing. I don't have the exact numbers on hand, but basically it is like so:
The bq reports 98% remaining. If I have LCD max brightness, OPP5@1Ghz, wifi on, the tps reports some voltage X.
After a period of usage, the bq eventually reports 92% remaining, at which point I put it into low power mode (OPP1@125Mhz, LCD and wifi off), wait a minute, and request the voltage from the tps, it once again reports approximately X. Under heavy load, bq saying there is 92% remaining, it is a voltage noticeably lower than X; under minimal load, that 92% is X which is the same as what the bq reported as 98% when it was under heavy load. Understand? My conclusion was that the battery has actual voltage Y, but depending on the load the tps reports it as lower than X; meanwhile, the bq is somehow getting the actual remaining level, either by determining what Y really is or some other means (I haven't looked at the bq code, so I don't know its inner workings as well as I've figured out the tps)
And I know it isn't just an averaging thing, because I've watched it drain out at various loads starting at 100%. Under high load, I let it drain out to 92%, measure the voltage, set it to minimal load and measure the voltage again: those voltages are consistent with if I had charged it to 100% and left it in low power mode until the bq also read 92%.
The effect of this is in the way the tps does the top up charging. When it detects the battery is as full as it is going to get, it stops charging until it drops below voltage level 3, as measured by the tps. In my experiments, I adjusted voltage level 3 (and 4) to be that voltage X. So if it charges to 100% and then stops, and I immediately pick it up and start playing mupen64, the charge light will kick back on at 98% after only a few minutes, however if I leave it in low power mode, the charge light doesn't come on again for hours, when the bq chip is reporting 92%.
I don't think this is really a problem, it just surprised me when I first started experimenting with it. I wanted to get your opinion on the top up charging though: under the current default values for voltage level 3 and 4, charging doesn't restart until about 86% under high load, and 80% in low power mode. This is far too low in my opinion: you might plug in to charge at 90% and wake up the next morning to find it is at 88% and conclude that there is a problem. The values I posted into the bug report keep it above 95% in low power mode, and automatically start charging even at 100% when under heavy load. I'm just not sure if that's a good idea.
