I run 55 watt auxiliary lights on a 2 year old battery with no dead battery issues. I'm wondering if low 12s are normal for idle. As the others posted, it's a great idea to thoroughly clean the battery terminals and connections. That's ususally the first place to start.
As you probably know, batteries don't store well. If the one you bought has been on the shelf for a while, it may be weak.
From Consumer Reports:
http://shopping.yahoo.com/premium/consumerreports/silver.html?id=95700426
