Mine is a garage queen and had been sitting for 23 days when I went to use it, the battery was so flat it wouldn't even unlock the doors! I had to meet some one at a certain time so I put it on charge and took my DD, I was back in a couple of hours, the car started and I took it for a 20 minute drive to charge it up.
After 5 days the battery is at 11.97 volts. My plan is to purchase a 6 or 7 stage battery charger to try and rejuvenate it, I know I'm up for a new battery but at least then I will be able to better look after the new battery. End of the day the original battery has lasted as long as I would expect it to, it's not the batteries fault it didn't get a lot of use.
I was wondering though how other 2011 batteries were holding up (or not).

 

My car is a 2012 and I changed the battery 6 months ago.

 

My 2011 v6 arrived in May 2010. Original battery with 24,000 miles.

 

My battery died last winter after the car sat for about a month to 2 months.
Car was delivered/bought August 2012 so the battery only lasted about 2.5 years.
Had it replaced under warranty by the local dealer.
I now have a dual-battery Battery Tender that I use for both Mustangs

 

I have 2 Deltran " Battery Tender Plus " units. ( 10 year warranty )
The guy who recommended this to me has 8 of them, claims he gets 8 to 10 years out of his batteries.
The 11 & 14 aren't DD's, when not being driven are on the tender.
The battery in the 11, ( delivered in July 2010 ), cranks just like brand new.
.

 

the battery in my 2011 was dead this morning, today was the first time driving it since last Thursday before the blizzard hit us, I had started it last Sunday, today it was nearly all the way dead. I figure its about time for a new one, 5 years is about the expected life span, some even go before that

 

Mine lasted roughly 3years and about 30k miles.

 

I have had good luck with the Motorcraft batteries in my past 2 Mustangs. My '06 still had the original battery in it when I traded it in July of 2011. My Boss still has the original battery since July 2011 & it sits through the winters. No battery tender, but I do start/run the car every week or so.

 

Arizona heat kills batteries. They usually go dead without warning. I replaced mine last September before it died.

 

The battery in my '11 is still going strong with 23K miles on the car. I drive it about once a week, and there are times it sits for as long as 3 weeks. That being said, considering the age I may go out there this morning and the battery is flat as week old beer.