Charged batteries have more electrons=> more weight,
Empty battery=>less electrons=>less weight.
You can also spin batteries to check if they are charged:
If it is full with electrons, then the battery will not wobble, since the mass is distributed equally through he whole? battery.
In case it is discharged, then it will wobble, because the electrons will shift the mass center...
nice try ^^
a corpse in free fall gain a speed
that speed....don't depend of the weight
it depend of gravity (ok it change from heigh...you need a lot of difference to see something :p)
a cannonball and a feather fall at the same speed in vacuum
so, it depend of air resistance (no luck a empty and a full battery have the same form or there is not enough difference)
IF you see difference when you let fall 2 battery ,it's because you don't blet fall at the same moment or the don't let fall from the same angle