Mike, if you only want to move the tractor for display purposes, I'd buy or build a lithium 36V "suitcase pack"- IF you don't have a ready supply of 20V or 36V("40V") lithium power tool batteries.  I've moved one with a stack of 20V DeWalt power tool packs in a 2S configuration, but a 36V battery in a portable configuration would also be useful for ET accessories to be used away from the tractor.   I also made a portable pack with a single stack of 5 salvaged Nissan LEAF modules.  

Dewalt 20V batteries are safe discharging for several minutes at 10 amps, so 5 of those in parallel, 2 in series would move the tractor around nicely and even allow a 50 amp 36V load for demonstrating the mower in 'normal grass'.  

Good Luck!

-Jay Donnaway