The Shamblers charge up routine goes combine:
Ring of Shocking Grasp 1 per round x 10 per minute x 60 per hour , and
Immunity to Electricity (Ex)
Shamblers take no damage from electricity. Instead, any electricity attack used against a shambler temporarily grants it 1d4 points of Constitution. The shambler loses these points at the rate of 1 per hour.
= 600 x 2.5 = 1500 real points of Constitution.
iirc - a Dwarf Sorc gets an ACF around level 9, to use Con as their bonus stat = even sillier.