There are plenty of times when you want to run a 12-volt automotive piece of equipment outside of a car. You could be developing an electrically run system (eg a water/air intercooler where you want to bench test the pump) or even running a car sound system component (with the price of used AM/FM CD players, taking this route can make for a very cheap workshop sound system!) Or maybe you just want to do some quick tests to confirm that something car electric works - an electric radiator fan for example.
