Rep Power: 0

I have had my boss load alternator for almost a year now and about 2 months ago it started spiking at 20v. So i took it to Alterstart in dallas (horrible customer service by the way) and they tested it and replaced the voltage regulator.
After installing it, I was getting a constant 14.4v out and was a happy camper for about 2 or 3 days.
Recently i started dipping down to 11v and rarely higher. Tonight it was bad so i checked the output for the alternator with a multimeter and it was pushing out 15.3v which is good. What would cause this to happen. I have an Optima Yellow top and both the alternator and battery are a year old. The output wire is 4 guage so it can carry everything fine.

I am really at a loss for this one. The only thing left is a bad battery? Either way they are both kind of expensive to fix. blah.
thanks for the help in advance.

 
Rep Power: 263

15.3V @ the alt then??
And where is the 11V reading coming from, the battery or elsewhere?

 
Rep Power: 0

15.3 off the alt.
and the 11 readings are from the radio fuse and the battery itself, while on the alternators power
and thats while revving, not too sure how high i was using the throttle under the hood. probably around 2-3k as usual.

 
Rep Power: 263

Set your meter for voltage, put your red lead to the positive alternator output and black lead to the positive post at the battery while engine is on. Let's see how much drop you're getting for sure before the batt.

 
Rep Power: 0

also, check the alternator fuse under the dash, i had the same problem, even with new battery and alternator, and it ended up being the fuse, check it, itll make the alternator show a low charge, even if its good

 
Rep Power: 291

check for corrosion on the battery terminals as well as the alternator terminals.