Yeah, that's the trouble, and it's why I've been sticking with this 22-ton Huskee chassis, despite having mostly out-grown it. It's light, it's easy to move by hand, it tips vertical in about 5 seconds... all good stuff. Really, if it had a larger tank and larger bung on the tank outlet, it'd be the perfect machine.
I have thought about just cutting one broad wall open on the tank, and welding my own tank extension onto it. I'd do the bung fitting at the same time, stepping that up to 1-1/2" NPT. But it might be easier to just sell this one and buy a 35-ton splitter chassis, as all that'd need would be a cylinder "downgrade" from 6-inch to 4-inch.
As to electric start, I solved the problem by putting a 50A connector on the splitter, instead of a battery. I bought a 15 ft cable set for all of $15 - $20, cut the big allegator clamps off each end, and mounted the same 50A connectors on each end of the cord, and then I mounted the same connector with direct battery connection (thru fuse) to each tractor. On a cold morning, I just park the tractor next to the splitter, plug in the cord, and start the splitter off the tractor battery. Never need to worry about maintaining a battery on the splitter, and no added weight while moving it.