This same story is repeated with all sorts of different vehicles. The most frequent Jeep stories on this site are not relevant to your late model Commander; they are usually found on the older Grand Cherokees.
A battery cannot be effectively tested for reserve power with a voltmeter; as a nearly dead battery will still have close to full voltage when it is not under a load. Try turning the headlights on, and watching their brightness while you try to start the motor. If the headlights go out or get very dim when you try to start; the battery is either worn out or discharged, or the battery cable terminals are either loose or need a thorough cleaning and tightening.
I would also recommend charging the battery with a battery charger; and then seeing whether it starts the motor. If the battery starts the motor after being charged; the alternator has probably gone out. This would lead to the battery gradually becoming discharged while driving; until it reached the point where there was not enough power to run the fuel injection. At that point, the motor would quit, and would not restart.
If the lights stay bright when you try to start, while the starter does not run; the neutral safety switch, starter or starter solenoid is probably defective. If your Jeep has a manual transmission; there is a clutch pedal switch instead of a neutral safety switch.
It is somewhat unlikely (although still possible) that it was caused by either the starter solenoid or the starter relay. It is more likely that it came from the neutral safety switch. The neutral safety switch, located either on the transmission linkage, or the transmission housing, is designed to prevent the starter from operating unless the shift lever is either in Park or in Neutral. Sometimes this switch is not aligned precisely enough with the shift linkage. In those instances; it occasionally may not be activated when the shifter is moved to Neutral or Park. Other times; it may only work in one of those positions; but not in the other.
My catalogs still do not list neutral safety switches for 2007 Commanders; but just for illustration, here is a link to a photo of a neutral safety switch for a 2003 Grand Cherokee: (http://www.rockauto.com/catalog/moreinf
o...). These switches are made in many different models; sometimes two very different switches are used in the same model year; depending on the type of automatic transmission used with different engines. It is sometimes possible to adjust the switch position by some careful filing or bending. On the type of switches which thread into the transmission; it may be possible to cut the shoulder on the switch body down; or weld or chemically bond a small extension to the part that is intended to contact the lever inside the transmission. An enterprising machinist would be the type of person to contact about this. If your car is still under warranty; a Jeep dealership may be able to replace the switch for free (although I wouldn't hold out much hope that another part from the same mass produced assembly line would be likely to work any better).
A more effective solution would be to have an electrical specialist simply connect the wires for the park/neutral positions together; thus bypassing that part of the switch. This would enable the motor to be started in any transmission position. (there is also a reverse sensing position on many switches; which activates the back up lights, so the switch cannot be totally bypassed). But this would not be safe for some drivers; as it does create the possibility of the car being able to start moving in some gear positions as soon as the motor begins to run. However, those who can reliably discipline themselves to either keep a foot on the brake whenever starting the motor; or only starting when in Park or Neutral, can do fine with this modification.