i have the same car, and i have these issues also i dont have a big 3 upgrade tho, i have a new 180 alt new gruop 34? or 91 battery whch ever one is made for the charger, but im running 3k watts at 1 ohm, i even have a second battery in my trunk, my amp is grounded to my negative originall battery terminal and the second battery is grounded somewhere else on the right hand side of the trunk, 2 batts and a new alt and my light dim also. i would honestly get a bigger alt maybe? then do a big 3 upgrade. thats what im planning on doin, i was actually surfing here see if any other charger owners have this issue with new batts and alt's but you havent gotten past to where i am right now, although my second battery is quite old, its and old SVR battery liquid not gel im talking maybe 4-5 years old. still does the job tho. lemme know if your problem gets fixed when u get a new 2nd battery.