5000mAh 18650 ?Seriously ?That's obviously fake. No such thing as an 18650 with capacity above 3700mAh.Yes, the weight difference makes a clear fake too, but it's not everything.I explained things in more detail here: https://xaeus.wordpress.com/2016/09/08/how-to-identify-18650-cell-capacity/
I like this, but you should add a note:Your solution will work only if the cell surface contact at the poles is perfectly flat. If it is not, which is the case with the majority of ripped-from-laptop-battery cells, the contact will be unable to provide sufficient current for many applications because the magnet will touch the cell only on a surface of fractions of mm. Yes, a LED will light, but something that drains high current will not function.