I have used the FORD OEM charger that came with the FGT since January 2006. Every year , all winter, spring and fall. Just plug it into the Cigarette lighter.
It even has a long enough cord that no extension cord is needed all the way to the front of my garage. It is on my FGT in the garage as I write this. I just went to my garage and checked... and it is happily doing its job...
Never a dead battery , never a gage issue. Works like a Ford Engineer designed it.....
I fail to see the debate and chuckle each time I do.... just use what Ford gave us...
andy (ajb)