The battery will be at 12.6 volts if it's fully charged. 12.0 volts means it's good but discharged. Less then that means it has a shorted cell and must be replaced, or it's really really discharged. A jump-start might not work when there's a shorted cell in your battery.
With the engine running, the battery must measure between 13.75 and 14.75 volts. If it is low, the generator is not working. That might have a relatively inexpensive fix.
Start by measuring those voltages. All you need is a very inexpensive digital voltmeter. Harbor Freight Tools has them on sale all the time for $5.99, and sometimes as low as $2.99. They work just fine. If the system voltage is low, the computers on the car will do weird things. No point in looking for an engine running problem until the charging system is working properly.
Saturday, March 3rd, 2012 AT 10:00 PM