I have an '05 Carrera w/18k miles that occasionally won't crank. It usually occurs after driving it for 10-20 minutes and then attempting a re-start within 15 minutes. Hooking up a battery booster starts it right back up. Checked the battery after sitting overnight - shows about 11.5v. With the car running - I'm seeing 14.0v. I haven't had a voltmeter handy when the problem occurs so I'm unsure of the reading. I'm suspecting the battery though the intermittent nature of the problem has me second guessing. Any ideas? thx in advance.