Hey guys,

I just got this battery app the other day, its kinda cool

So my phone says it's done charging (via usb),.. and the led light is green... but this graph tells me its only 3/4 charged... total fail!?

http://www.flickr.com/photos/2962996...5928/?edited=1

nope. zero fail. the voltage seems to be as high as it can be when battery is operating safely.

the battery percentage is a bit like measuring horsepowers of a car by sitting in the car at showcase and not driving a meter with it.

So I left the usb charger connected overnight, and now this:

http://www.flickr.com/photos/2962996...9939/?edited=1

What the heck...

Could someone explain why this is the case? Why isnt the maH reading out of ~1200 and the percentage how much battery you have left?

percentage and mAh are only rough estimates calculated from voltage data. Just as I told you with the car metaphor

Alright cool. So between picture 1 and 2 the voltage stays the same. But the precentage and mAh differ drastically. How do we explain that?

You just quoted the answer. Because they're "rough estimates calculated from voltage data".

because percentage and mAh must be calculated from something like this:



and the percentage & mAh are straight lines from 0%, 4.2v to 100%, 2.8v. How would you calculate percentage & mAh from that source data?

plus the voltage measurement isn't very accurate I think with any pocketable mobile device (except flukes) and the data n900 collects has a lot variance (the voltage line has a lot of peaks).

those graphs are for a set of constant current loads, the n900 puts a highly varying load on the battery

I would bet the voltage measurement is actually the only bit of data that is on point. You are correct about having to calculate the remaining charge based on a plot or lookup table. But also you should know that each battery is slightly different to begin with and the curves change over time as the batteries are charged or discharged.

The percentage is directly calculated from the current, which in turn is estimated from the voltage.

In the end its really a very very rough estimate of whats going on. The only real indicator at any given point is the voltage, and that is when its not being charged.