Most of the comments here completely miss the fact that difference in the OP appears after charging, not after using. It doesn’t matter if one is primary or not, they both had the same amount of time to charge from 0%, so they should be the same.
This is if they have the same size battery, which might not be the case if one needs more to work.
Also, the state of charge might be inaccurate, it might report zero on a secondary one if the primary is also down just so you put it both back on charger so they equalise.
Also it might all be bullshit and we’re speculating on it randomly.
Most of the comments here completely miss the fact that difference in the OP appears after charging, not after using. It doesn’t matter if one is primary or not, they both had the same amount of time to charge from 0%, so they should be the same.
This is if they have the same size battery, which might not be the case if one needs more to work.
Also, the state of charge might be inaccurate, it might report zero on a secondary one if the primary is also down just so you put it both back on charger so they equalise.
Also it might all be bullshit and we’re speculating on it randomly.