I wired in a couple more Head light globes and got the current up to over 10A which was great again with no noticeable heating of the FET, But!

Even by limiting the current to 10A the battery voltage rises quiet fast reaching 13.8V and then turning off and dropping back to 13V again very quickly - while everything seems to be happy Im not sure what he impact on the batteries will be as they will be pulse charged with quiet high currents.

Im thinking a large inductor in between the switching FET and the current sensor would limit the current rise through the FET and into the batteries then I would need a diode to ground and I now have a buck converter :-)

So much for a simple charge controller