Land your voltmeter across the relay contacts (+ battery post & starter lug) and crank it. It should not show more than a couple volts drop while cranking. I'm really surprised your battey is not damaged. If the problem is intermittent and you are sure the battery is good (put the volt meter across the posts while cranking, should read ~>10 volts while cranking) then it might be something else. Land the volt meter on the coil of the starter relay, if when it "misses" the voltage is +12 then the realy is intermittent and need replacing.