Ghurd's controller has nothing to do with the battery AH rating. What matters in the setup is the battery AH rating as it compares to how much your dump load dumps.
For example, when I originally discussed it with him, I was using a 7AH SLA battery. Using 8 of his resistors dumps about 11A at 14.5v if I remember right. That is nearly 3 times the C20 rate for that SLA, meaning it would run the battery down very quickly when it dumped.
The point in that rambling in the paragraph above is that there is a relationship between the batteries and the dump load itself. GHurd's circuitry just CONTROLS it. The individual FETs on the controller handle 6A very easily, and you can output to MANY FETs.
The short answer: I use his controller on a 12V, 220AH battery bank. Works great. Glen is the man.
