gauges

i am thinking of putting some gauges in my car. i want to put a volt gauge in my car b/c sometimes i like to listen to music but i don't want to turn the car all the way on and let the car idle for such a long time but i dont want to leave the system on and the car off to where it drains the battery. is there any brand that someone could recommend and i am looking at a digital gauge are these any good or should i stick with analog. also is there easy second gauge that some one can recommend for me to get.