Nokia Battery Monitor 3.1 update and the mysteries of battery discharge

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Nokia Battery Monitor has been something of a staple of the Symbian world in the last couple of years, providing a large-fonted, colourful guide to the state of your smartphone's battery. However, with new batteries coming along with slightly higher nominal voltages (quoted at '3.8V' rather than '3.7V'), the existing utility was demonstrably inaccurate. I've been testing the new version 3.1, now available, and seems to behave slightly better on the Nokia 808, but more data points are welcome from AAS readers.

Whatever the improvements (or lack thereof) in Nokia Battery Monitor 3.1, I thought the whole subject of battery charge estimation deserved a little comment. Note that battery voltages are never as easy to pin down as you might think, varying by temperature and load. They also vary according to the state of charge, typically starting at over 4V when full charged, quickly dropping to the nominal voltage (around 3.7V) and then dropping only slightly until they get to the last ten percent of so of charge, at which point the voltage starts to drop more quickly.

So when a battery is quoted at '3.8V', it just means that the chemistry has been improved slightly in such a way that the majority of the cell's discharge is at around 3.8V rather than '3.7V'. The maximum and minimum voltages will still be widely spaced and the voltage is never constant. The result is that estimating the actual battery capacity remaining is something of a black art. 

And isn't helped when the utility has the characteristics of yesterday's '3.7V' cells hard coded in, with the result that I'd charge my Nokia 808 and would be able to use it for a full hour while the charge was consistently shown as '100%'. This new version 3.1 of Nokia Battery Monitor seems to start decrementing the charge level sooner, though it's still not perfect. More data points welcome from readers!

To illustrate the issues involved in the estimation of charge remaining, I did some tests over a full discharge cycle with my Nokia 808 PureView (with the BV-4D '3.8V' cell in place) and noted the percent values reported by both Nokia Battery Monitor and the voltage reported by the utility PhoNetInfo:


As you can see, trying to produce a meaningful linear readout of battery state from such an irregular battery voltage isn't trivial. My guess is that a utility like Nokia Battery Monitor has its own internal model of the red line above and compares the measured voltage to read off roughly where the charge state has got on the curve. 

You can grab your own copy of Nokia Battery Monitor from here for free, and more data points welcome - how well does the utility handle a full charge and discharge on your Symbian smartphone?

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