[atreis]

On the tray that's there: No. You can probably fit two there, side by side.
On a custom tray that you build to sit on top of the frame: Probably, but it would take some doing to secure properly.

That said, unless your tongue is currently much lighter than it should be, it's really not a good idea. The battery it came with probably weighs 70ish lbs. A single GC6 weighs 90 lbs. Putting four of them there would add ~300 lbs to your current tongue weight - not good. Two on the tongue might be okay - depending on what your tongue weight is currently. Tongue scales aren't all that expensive at Amazon, by the way. Your tongue should weigh between 11% and 15% of the total trailer weight. Going under is REALLY bad (uncontrollable-accident-causing-sway type of bad) while going over could overload your tow vehicle or hitch.