I don't recall the clamp configuration but when I replaced the battery in my 2007, it tightened up fine. The posts are standard on all batteries.

 

I found the problem - last summer, when I replaced the battery, they put the clamp back on wrong. The beveled slider, that gets pushed against the post clamp was turned around backwards. So, as you tightened, it pushed that lower block AWAY from the battery post... idiots! Frustrating that it could have left me stranded, even worse that it could have left my wife and kids stranded. I don't even understand why they took it apart (I had to disassemble it to correct the problem). Pics below are the corrected clamp.

http://oesm.org/images/dlinkoz/IMG_9873.JPG
http://oesm.org/images/dlinkoz/IMG_9874.JPG

So, even if this doesn't fix my original problem, it at least corrects a problem. In hindsight, it makes sense that I've noticed that my headlights dim a lot while driving (they didn't do it at all during my test drive a few minutes ago).

 

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I am happy to hear you were able to fix the issue. If you continue to have the battery drain issue, consider taking the vehicle in for an inspection.

Please keep us posted.

Louis
GM Customer Service

 

(1) Good reason to change out yourself.

(2) This can be a sign of an alternator going TU or a bad connection somewhere.