Most batteries won't start a vehicle with less than 10.5v, 9v is probably the lowest a 12V Starter circuit can muster and it will barely go at that. Something is wrong with your meter if the car starts fine and its reading 7.12v
Also if you have the vehicle running and you check the voltage, you should be seeing about 13~14v, this will let you know if the meter is accurate. Most cheapo meters are very inaccurate, here's a section of the stickied
http://www.toyota-4runner.org/4th-gen-t4rs/132953-toolbox-how-use.html that describes what I am talking about.
DMM (Digital Multi-Meter) and/or DVOM (Digital Volt & Ohm Meter)
~This is your go to tool for pretty much anything electrical, I recommend everyone try to have one of these in their toolbox for electrical gremlins. We'll go into detail about using this tool and the other electrical equipment in another section.
Lets start with defining the difference between a DMM & DVOM, a Digital Multi-Meter offers functions such as Resistance (Ohm), DC Voltage, Diode Checking, AC Voltage, Hertz, and possibly other types of measurements. A Digital Volt & Ohm Meter, can offer you pretty much the same, the difference comes down to semantics almost. Truthfully by definition, the DVOM will be more simplistic while the DMM is more robust. But a lot of people will use the terminology interchangeably. For the purposes of this section I will refer only to DMMs.
DMMs are relatively cheap these days, you can get a decent one from Harbor Freight or your local Autoparts store for cheap. But what about guys who's devotion to their all mighty Fluke 87 or 88? Is it worth the $800 or so to get a DMM kit from Fluke when I can spend less than $150 for something that does the same thing?
Well, again it depends on what your needs are. The main difference between say your cheap DMM and something like a Fluke 88 is quality, again you get what you pay for and in this case you're paying for accuracy and speed. The cheap DMMs are not going to be as accurate as their more expensive counterparts, granted most people don't need accuracy to the .000 of voltage or highly accurate Ohm readings; but it does help. The more expensive units will also have features such as auto ranging (will automatically scale the measurement, i.e. it will switch from Volts to Mili-Volts to provide better resolution.), retain lowest and highest measurement made, some will even make graphs for you! I personally love my Fluke 88 and it has been an amazing tool for many uses, in my experience you really should make accuracy a consideration in the investment of a DMM. Vehicles these days use as little as 1volt on their network lines, an error as little as .02volt (that's 20 mili-volts) can cause errors and light up the dash!
