Car won't start... PLease help

[whytry]

Went to take the car for a drive, would not start - low battery, put Sears charger, (the one with selectable 2,10 or 50 amps) I had it on 10, let it sit for about 10 minutes, cranked over a couple times but would not start, then shifted to 50 amps, (stated for starting) car started perfect and let it idle for a moment, jumped out of the car to unhook the charger and the car died... Crap, so I tried to start it and it cranked 2x but would not start. Put charger back on it @ 10 amps and let it sit for a couple minutes tried it again, cranked slowly then clicked and then nothing!!! Charger started making a funny noise so unplugged it all. Checked battery with voltmeter and it showed close to 5 volts!! Then went to pull headlights on and nothing worked at all in the car not even the dome light, went to battery shows 4 volts now and dropping... Took out of car and charged and went back to 12 volts, put back in car and began to drop again all the way down to where nothing would come on..... I switched to Ohms and it shows approx 4 ohms load on battery while voltage is dropping..... Unhooked battery checked terminals and showed 1....

I was putting new carpet and Fat mat in the car before this happened and before I put the seats in etc, I checked all the wires and it was fine, headlights worked, everything worked... Battery is an optima red top.....

HELP!!!