René wrote:

And now I will go on with my design of a battery charger that cuts off
the charging process based on weight increase of a charged pack.

Take a 12V, 100AH battery. That's 12*100*3600J = 4.32MJ. e=mc^2, so the
mass gain from flat to full is e/c^2 = 5e-11N, or about 5e-12Kg. Piece
of ****, but works better with bigger batteries.

Paul Burke