I have a 2007 Yukon XL that will start fine, even going 2 weeks between starts. However, twice in the past 2 months I've had it, the battery shows about 9-10 volts and it won't turn over. Everything else works, so it's not completely dead, just not enough juice to start. Battery is less than 4 months old. Wondering if it's something happening when I wash it, or is this a common problem with some 07 Yukons/Tahoes, etc? Some sites have said some diodes could be bad in the alternator causing a drain, but this has only happened twice to me and I would think if it were the diodes, it would drain all the time.