Battery '"Estimate"' percentage

[Vabe]

There have been many discussions about this feature and why it is hard to implement.
One thread you can find here:

Remaining Battery always 100% at start

Hi No matter how much voltage the battery I connect, the FC always interpretate the battery is fully charged. There is any way to calculate that battery porcentage from the input voltage? For example, Im using 6S battery, so the max voltage will be 25.2, that way if I plug a used battery, with 23V, FC could know that is not a fully charged battery. Thanks!

or here:

Battery monitoring accuracy / type

Hi all, I the last few years people are starting to use the Li-Ion 18650 cells to power their vehicles but these cells don’t have the same minimum limit of the Li-Po cells, they can go down to 3v per cell with relative safety for them. Well, regarding cell and battery monitoring I do think that the ArduPilot firmware can go easily much further with very little effort from the developers team, I am not a developer but I understand what can or can’t be considered as “relatively easy” for them. …