I have seen those Elements on the internet somewhere but can't find it right now.
However, I think A simplier, cheaper, and much easier way is to just do as Ghurd said in your previous post:
"Maybe a simple dump controller.
When the battery is full, the ignition is SHORTED and the motor stops."
I personally would try the simple way first as Ghurd said with a a 48vdc Relay like:
http://www.surpluscenter.com/item.asp?UID=2008031116350615&item=11-2337&catname=
The (control) coil of the RELAY is to be activated by the DIVERSION CHARGE CONTROLLER automatically when the Batteries reach full charge.
So you would hook the POSITIVE from the CONTROLLER DIVERSION terminal to the Positive of the RELAY COIL. And then hook the NEGETIVE of the Relay COIL to the system GROUND.
On the 5hp gas engine there should be the high voltage coil near the magneeto.
Jump a wire from the wire that goes to the coil and hook it to one side of the relay contacts and then hook the other side of the relay contact to the GROUND of the gas engine.
I can't promise that that particular relay will work though. I think it will. There is a slight chance though that the high voltage from the Magneeto coil could spark across the contacts of the RELAY and short the gas engine to soon. I'm not sure.
This is why you really need an Electrician who has good experience/knowledge with setting up Renewable energy systems.(Dump loads, etc.)
I have never actually tried this myself though.
Has anyone here ever set-up an automatic 'Shorting circuit' like this from a Diversion Controller in order to stop a gas back-up generator automatically??