I'll try to keep this simple. I have two ed nine.1s and one ed nine.2x for amps. I have 0 gauge wire from the front battery running through a 300A fuse under the hood to a 150A breaker in the rear, then to an isolater and on to a yellow top in the trunk. I recently added the second Nine.1 three weeks ago. I went a year and a half before that with no charging problems. One week after the second nine.1 was installed the yellow top went to around seven volts and when isolated completly does not hold any charge. I took the car back to the shop who installed the amp. They told me I just have a bad battery. So I took the battery back to another store where I bought the battery. They put an over night charge on it and said the battery wasx fine and blamed it on faulty wiring. Who is right here. The audio shop is pretty much saying that it is a coincedence that the battery went dead one week after doubling my power. Oh ya I do have a 150A alt under the hood. Sorry if this is confusing. I just want the problem fixed and the idiots around here just blame eachother.
i dont know how your stuff is wired up. it sounds like you have 1/0 run to the back and on that line is a 300a fuse under the hood after the first batt. then it sounds like you have a 150 breaker on the + by the batt in the trunk. well first with all those amps your going to be pulling more then 150amps.
the alt you have is only 150amp that would be ok supporting one nine.1 and the comp amp. but the second 9.1 is drawing to much current then that alt can produce.
sounds like you drained that yellow top in the trunk playing your system and your alt never had time to recharge it because you had your system on while driving.
the audio shop just said it was bad because it had 7v and they were lazy and probably hopping youd buy a new one from them. it also sounds like they dont exactly know what they are doing.
you need to install a volt meter and monitor your voltage at the amps.