Voltage dropping to 12.5v isnt good imo. With a 225a alt and 2500wrms amp on music (doubtful you even come close to that rms rating), you shouldnt really have considerable voltage drop. You went from a RF amp to Sundown. Sundown amps are no joke. You may want to consider upgrading or reworking your electrical wiring if needed. You might even need to look into XS Power battery up front and another XS Power battery near the amp. I have a feeling you are starving your Sundown amp. Maybe your enclosure foe the sub is less than optimal. Good luck Whats wrong with voltage at 12.5? Also, why wouldn't he have a considerable voltage drop? Assume at idle the 225a only puts out 150ish, the voltage is going to drop when the alternator is reaching its output limits. I don't see how he is "starving" the amp either. With the information the op supplied he changed amplifiers and upgraded to one with 2.5 times more potential output. Therefore the electrical requirement is 2.5 times more. But.........no additional electrical upgrades were done to support all the added power. 12.5v is basically the resting voltage of his battery. This means, to me, that his amp is pulling 100% power out of the alt and them dipping into battery reserves. Dead battery anyone? 13v or higher for me or my systems is turned down. There are many unknown variables here, but my opinion stands. Op, how hot does the amp get? Pretty hot I bet. I ran my previous amp with the stock 120 amp alternator for.... 2 years I believe without incident. Voltage RARELY dropped below 13.8-14V. The time between the period where I upgraded alternators and sold my amp was maybe 2 weeks. That means that I played my "old system (old amp and sub)" for about two weeks with the upgraded alt. Voltage was fine still, obviously. The battery was replaced about 4 months ago. It's resting voltage is 12.6V. Your logic doesn't make sense. Just because I upgrade amplifiers does NOT mean I need to upgrade my electrical if it is already at or above par. I do not ride around playing tones either, so The amount of time my amplifier will draw full current is VERY short. You know about the dynamic properties of music, etc. 225*12.5 (the LOWEST voltage it will drop to) =2812.5. And this doesn't account for impedence rise. And it doesn't include the current the battery has available!!!!! I believe my electrical system is not the problem. I do not mean to be offensive, I just get the feeling that this is NOT and electrical system related problem. My friend was running a SAZ3500D to two 18" Xcons on stock electrical (150 amp alt and one battery temporarily) and he could drop to 11 V!!!!! And it was still loud as fawk. Amp stays cool as a cucumber. However, the dustcap of the sub got quite warm, which lead me to believe I was driving the amplifier into clipping, which baffles me, because it does not feel like 2500 watts of punishing power. It barely feels like 1000 watts! Oh and ANOTHER issue I have is that when playing at full volume, my voltage will actually spike up to over 15V, sometimes giving me an error message on my Driver's Information Center. This is a very strange problem I cannot figure out. It happened with my old amp as well. Stupid PCM monitored voltage. I need to get my alternator internally reg'd I guess.