Up to ~1000 A constant current supply 10-40 VDC
So, use exactly what the big trucks use - big batteries - these can be charged (I think "trickle charging" might be a little of an understatement of course). Don't waste time and effort designing something that might take a year to properly engineer - use what the trucks use (or the buses, lorries, trains, planes or whatever).

You say that replacing the batteries is expensive - I bet it's cheaper than the effort to design a 40kW DC power supply.