I was helping a friend with his Quest that needed the PS pump replaced. Thanks to the forum, it is working again!
However, it sat in my drive for a week after a new costco battery was put in. The battery was flat after a week of sitting.
I charged the battery and tested the voltage not running and was about 12.5v. When running it is 13.1v. across the battery terminals. I pulled the fuse to alternator and it was OK. It looks like the alternator must be faulty?
Is there any other cause for this?
Thanks for any ideas? I'm happy to take it to O'Reilly to test if that would be useful?

That could be normal, the '12 Quest uses "smart" charging controlled by the IPDM. That also means the problem could be indirect, such as a bad battery current sensor. Check the voltage drop on the main cable between the alternator and battery to make sure it isn't a resistance problem. If that checks then you'll need a scanner with work-support to see if the IPDM is driving the S terminal properly and the alternator responds properly to it.