hi,
the feature to look for here is the availability of an "external redundant power supply". If you look at the back of the FGT (for example, in the datasheet) you will notice a 2x5 connector. Here 12V DC will be supplied from a FRPS. The 300D supports this, a 100E as well.
That said, I would contact FTNT Support to get their opinion on supplying your "own" 12V DC via this connector. Basically, it's got a + and a - pole, and the FRPS is a switching power supply like any other. So there's no magic here to feed power from a stabilized, fuse protected DC source (in my opinion).
The smaller models will draw up to 11.5 A, the bigger ones 17 A (Support should be able to tell you the rating for your model). IMHO supplying clean DC from a battery is even superior to DC generated from a switching PSU, so this might work for you.
HTH,
Ede (ede_pfau on forum)
