Why did you use an isolator? Unless you're operating portable, there is no need for one.
Originally Posted by K0BG
I guess I followed the recommendations from Sgc and just did it per that. They gave me the model number of the isolator to use and I just used it. I was afraid of the two batteries fighting each other when the vehicle was stopped. I know that they will be connected when they are supposed to be and disconnected when they are supposed to be.
It is a common misconception about lead acid batteries that the MUST be isolated. They don't depending on the application. What happens when you do is there will always be a lower SOC for one or both batteries depending on the isolator hookup.
As for the batteries fighting each other, that isn't true either. You can mix and match lead acid batteries as long as they are about the same age and/or condition. If one has a slightly higher float, they will eventually even out to the same voltage. The only isolation you need is fuses to protect the wiring incase of a short.
There is another over-looked issue too. The SG500 is a decent amp (I've owned four, and still have two). It will operate down to about 10.5 volts or so, but the IMD gets really bad under about 11.5 volts. In my mobile, there are two 55 Ah, Optima AGMs. The rear is fed from the front with #2 copper (+ and -) directly to the amp. The second battery is paralleled with the first. Both has 60 amps fuses in the leads. On dead carrier, 500 watts out, it takes about 30 seconds before the battery voltage drops below 12 with the engine at idol. On the open road, it never goes below 13.2.