Are you measuring battery capacity based on (charge current flow /time ) ? This may not be precise, depending on the internal resistance of battery, some batteries will take more current ( which is converted to heat during charging ) than their actual capacity is.

Hi, the calculation of the electrical charge is done exactly as you described it. In addition to the internal resistance of the battery, the comparatively imprecise time measurement via the internal oscillator of the microcontroller also plays a significant role. As a result, the displayed capacity is of course only a rough estimate in the end. However, I think this is still sufficient for most applications, especially since the main purpose of the device is not to measure the capacitance precisely. In my opinion, a measurement over the discharge cycle makes more sense anyway.