[oil pan 4]

DC jumps gaps much better than AC.
Higher voltage DC will also establish an arc and will maintain the arc until the power is turned off. When dealing with batteries this presents an obvious problem.

I have seen double voltage starting only on direct drive. But I have seen inverter duty motors that have the option for parallel or double voltage starting.
Double voltage starting on inverter motors is out there but I have not seen it.

My DC stick welder that I built runs up to 125VDC open current. It can throw a pretty good arc.

Also most wire is only rated to 600v.

For anything up to around 144vdc I would just use a normal wrench wrapped with electric tape and welding protective gear for making the energized connections.
For 100s upon 100s of volts NFP70 arc flash stuff should be uses which is pretty much like wearing a bomb disposal set.

If I were going to build an electric vehicle I would stay between 48 and 144vdc since it is relatively easy to work with and all the parts are off the shelf.