peak is a useless selling ploy stop thinking about peak and only think about RMS ... and you would need a 525A alt IF you had no batteries ... your batteries are what the amps and car take the power from ... your ALT is what keeps the batteries charged ... if the batteries had 1AH then you would need a huge ALT .... but they dont they have many AH so they stay charged for a good long time and your ALT keeps them charged ... you will be ok with a 270A alt and batteries. My car right now had a d3100 and stock alt ... i can bump for a good long time full tilt with ~ 3000 watts and i dont voltage drop below 13V untill after about an hour of playing ... i will soon be getting a second 200A alt making 270A .... just get a good 270A alt and some good batteries, hook it all up with good wire and you will be PERFECTLY ok to BUMP for a long time !