RE: Best Way to charge gel 7a 12v on way to field?
The only problem I see with the fused direct connect is that if the 7 Ah gell cell is significantly discharged it might draw more than one Amp and then the fuse will blow. Then you'll be left with an uncharged battery... which would defeat the whole purpose.
You could discharge your battery then measure the max current when you connect it. Even with a measurement to see what's happening, I think I'd just hook up the battery and fuse and see what happens. The fuse will protect the battery (and car). If you find it never blows, then I'd say your fine. You might want to carry a spare fuse with you figure this out.
If somebody knows the internal resistance of a 12 7Ah gel cell we could figure out the answer.