I made a try with a 7 plates dry cell + 2 really big neodymium magnets (7 Newton).
My cell, with the same electrolyte, same amp(18) produce a lot more HHO with magnets than without.
I did like this
M+ magnet positive side
M- magnet negative

M- - N N N N N + M+

The water flow was a lot faster, I didn't check the temp, I got no way to do it at home.