The answer is...well, probably. You see, when a metering system is calibrated to the battery, it's calibrated to THAT unique battery. NO two batteries have the same signature (maximum voltage at full charge, minimum voltage at the proper fall-off signature, discharge curve)...no two have the same capacity, even if off the same manufacturing line, no two batteries have been charged and discharged exactly the same way, so they will be at different points in their respective life cycles. Different variances in the concentration levels of the Lithium paste used in these batteries, varying thicknesses and levels of purity in the metals, varying levels of manufacturing techniques and precision, varying temperatures and humidity during the manufacturing process...the possible variables are infinite, and with each differing variable, a different battery is created. Take any two right off the line, place them on a battery testing station and they will produce different specifications. That's why there are "tolerances" such as +/- 5%.
It's really not much different than saying identical twins born only seconds apart, have virtually 0 chance of dying only seconds apart. Each twin will live different lives, eat (charge) differently, burn calories (discharge) differently, and as a result, one will die significantly sooner than the other. I know the analogy is quite a stretch but it's easier to comprehend.
Now, if you start with two identical batteries, and you use them interchangeably and always rotate them, always charge them in the same way, and always resume charging at the same point of discharge, they will tend to "moderate", becoming very similar in voltages and current capacities, and as a result, the metering system will be relatively accurate for both. On the other hand, if one is a standard battery and the other is an extended battery, all bets are off.
