I know this is an old thread, but I feel the need to make everyone aware.
Those $20 stinger meters do NOT list the accuracy or the response time. So you are basically buying a name brand with no specs. Like buying a kicker sub that doesn't list the wattage or frequency response.
Anyways, these ebay meters are $5 shipped (at most) and are 200ms response time and 1% accurate.
They are MUCH smaller than the huge stinger meters, so you can mount them ANYWHERE. They even have smaller ones if you need it but these seem to be perfect and the trim looks nice in the dash and there is no logo or writing anywhere.
0 56" Digital Voltmeter Green LED Panel 3 2 Wires DC 0 100V 4 30V Power Monitor | eBay
This one is >=200ms response time.
Make sure to get the 3 wired ones because those have the auto on feature (hook one of the wires into the ignition or remote out from the head unit. I used ignition because I like to see what my battery is at before I turn the car on)