DMM (Digital Multi Meter) are always good to have a round for many things.
Like for your car battery, checking lights in your car, etc.
Home: Checking to make sure that voltage is where it's supposed to be.//content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif
Can't imagine NOT having a DDM around. Use it all the time.