Rep Power: 0

I recently purchased this 2002 civic ex and I have only driven it during the day until last night. It was cold and rainy so I had the following on head light, radio, wipers and heater. Everything was working just fine until I turned on the rear defroster and within 2min the battery light came on. I would give it gas and the light would turn off and as soon as I letoff gas it would turn back on. After about 5min of the battery light being on I turned off everything except head lights and the battery wouldn’t turn off. Got to my location and shortly after the car died and wouldn’t start any more. Car had some power for some lights etc but not enough to even get a click when trying to start it.

A few weeks before the issue I replaced the alternator and the battery is less than 2 years old. The bolts are tight and belt tight. At idle the car puts out 14.4v and when I turn on all (stated above)except rear defroster it seats at 14.2v. The second I turn rear defroster on it drops down to 12.2 and will continue to drop volts every 40sec-1min. It was high 11v before I turned off rear defroster and it climbed back up to 14.4v. I have replaced the load detector as well. Please help!

 
Rep Power: 518

Is the belt tight enough the alt pulley can't slip under load??
If so, replace alternator again

 
Rep Power: 0

 
Rep Power: 518

If it fails a test, sure.
But If it doesn't fail their test that does not mean it's good.
Then test to figure out why the alternator can't keep up with the cars demands.