Answering your questions:
About the regulated supply, I suggest everyone with any sort of DYI project in hando to build one. ICīs like the
LM317 make an easy task to build a cheap and very acceptable regulated supply.
About the residual current draw: Thatīs what it is, residual. As such I donīt bother much about it since I donīt usally have the device connected when the engine is not running.
About the cutout voltage, I really donīt know what you mean...
Cheers