Here are my thoughts and I must add I’m far from an expert on battery capacity and voltages.
455v in 44.5kw/hr battery produces 97.8amps
If the current remains the same but voltage drops to 450v then capacity falls to 44kw/hr losing 0.5kw/hr on capacity or say 1.5miles. MG are also able to tweak the usable capacity so that it remains roughly the same. I’m not sure if monitoring small voltage changes provides any real value - if there is a 5v difference on some cars the real-world impact would be negligible if any. ?
I don't think the amps calculation is relevant for figuring out the battery capacity.
We know (well think!) the car has a 44.5KW/H battery capacity.
Bosch power tool example. 18V battery, but they advertise e.g. 3AmpHour battery, so you'd have to use the formula to calculate the batteries actual power capacity - 54Watt/Hour battery.
It can draw whatever (in reason) it wants in amps depending on you right foot. If we knew what voltage the motor was, based on the real-time amps reading, you could calculate what the real-time consumption was in KW, that'd be interesting...
Batteries as we probably all know, output their highest voltage when are fully charged and then the voltage goes down as their charge lowers - shows up very well with the old ni-cad/ni-mh batteries. Lithium batteries tend to keep outputting their nominal voltage for most of their capacity and then only when they get to a low capacity does the voltage output drop.
If the total cells voltage output at "full" charge, was 455 previously, then now being at 450 must mean the batteries have not been charged as much as they were previously.
But we will never know how many KW the battery really is charged to. Is the so called specified 44.5KW/H battery when it's charged to the point of outputting 455volts, or were we putting more power into the battery previously and it was say storing 45KW/H before, and now with them stopping the charge at 450volts output is that actually storing 44.5KW/H in the battery.
I guess, if we knew what cell the battery pack was made from, and we had detailed information from the cell manufacturer of the voltage vs what power stored (I think they produce a graph for this usually), then we could work out the actual capacity, knowing how many cells are in the battery pack - assuming all the cells were balanced. But realistically, multiplying all this up, the chances of getting an accurate result at the end of it, I'm not sure we'd be able to accurately know what the capacity was at 450 vs 455volts.
Well that was a lot of waffling on and, I'm not expert, I have just read a lot about batteries over the years!!!!!!!!!