You are lucky if the range estimate from any system is accurate within +-50%, so I really would not get hung up on it - range depends on too many variables (terrain, assistance mode, tyres, height gain etc) that a simple voltage check cannot take into account.
If you have a 2019 giant ebike, you can upgrade to the new ride control one with ant+ support. I did it, and now my xplova x5 evo shows all range, battery and mode information
I have found this app is extremely good for my giant explore E+2 its called (IPbike) I got my bike up to 96.8kmh I have not installed any of the new electronics