Just to add, 13+ Volts is the critical number. For the battery to charge, the charging system, basically the whole electric systems, voltage has to be higher than the battery voltage. If the voltage for the charging/electric system is lower than the battery, than the battery will take up the slack and provide voltage/current, and drain the battery.
The Battery is 12VDC nominally, a fully charged battery in tip top condition might show 13VDC and the voltage drops off as it drains.
So, like 99XJ says, if the Charging/Electric system shows 13+ volts that means it must be charging the battery.
Also check the voltage engine off and engine running (i.e. just battery vs alternator supplying power), the charging/electric system voltage should always be higher than the battery in all cases, or you have a problem.
The battery looking warning light on the dash, is really a charging/electric system fault warning light. They make the light like that for the typical idiot consumer, because all they can understand is that the battery is likely going to go dead.
Typically, the figures may be different for the Commander, but close, it goes off if the voltage is too low or high, or the PCM recognizes that field control of the alternator is NOT working right (which the most likely cause of that is a bad alternator and will result in voltage being to high or low). Typically volts drop below 9VDC or above 15VDC it will set off the light. If you charging/electric system drops below 9VDC, your alternator is NOT supplying enough current (there can be all sorts of causes for that, including things that can happen with a perfectly good alternator) and the battery is draining very quickly.
If the light stays on because of low voltage you only have a 10-30 minutes before the car will go dead (depending on the electric load on the battery, i.e. headlights) and the battery may be too drained to restart the motor. Sounds like that is exactly what happened to you.