Magnets.....OT?

Hi,

I hope the list Mom will forgive my OT but it is going on a CNC grinder.

I have a magnetic table, for surface grinding, and the magnets have become
very weak. I have been told it is possible to re-magnetize them by using a
car battery and a coil. Can anyone tell me how? ie. How many turns and
thickness of wire?

Regards,

Terry