A buddy has a 2005 G35. He says it sounded like it was starting slow, so he replaced the battery, and dove it a few places with no warning lights. Then he parked it overnight and it wouldn't start the next day.

I'm guessing there's a parasitic drain. I know the radio was a common problem on the '03, but I don't know on the '05. Is there a common problem on the '05 that drains the battery?

Out of 22 cases in Identifix for G35's from 02~08, the breakdown is as follows:
6 - Replaced Battery
5 - Replaced/disconnected CD changer
5 - Replaced Amplifier
2 - Replaced Radio
2 - Replaced BCM
1 - Replaced ECM
1 - Replaced Power Seat Controller

Interesting. Thanks!

I finally got a chance to look at the car last night. It's not what I thought it was. The battery only drops from a little over 12V to a little over 11V when the starter is engaged. The starter makes a noise, but sounds like it's turning against an immovable object. We also saw a small puff of smoke from the right front area of the engine bay on one attempt. I told him he needs professional help unless he's cool with renting something for a long time until I can get a chance to look at it, and that would still involve a tow to my house - so he's going to find a shop. Coolant and oil looked fine, so no milkshake of death. Maybe it's just a bad starter?

That would be characteristic of high resistance in the brushes or solenoid ring, or just a bad connection. If the starter was healthy and the engine was resisting, you'd get extreme drop, 8.5V and lower. In this case, the brushes, ring, or cabling is preventing full voltage from reaching the armature, hence a smaller-than-normal drop.

Cool! Hopefully it's just the starter.