Charging Problem?

Background:
The battery is a Sears Maintenance Free Die Hard and probably is only about 2 years old. Every year I park the Stang for the winters and put the trickle charger on it the day before I'm taking her out of hibernation. I haven't disconnected the battery over the winter months.
She's been fine until this year.

For the first time, this year I have an issue with starting the car right after shutting it off - it won't. It's as if the battery is drained. If I wait a half hour or so, it'll start but, again, as if the battery was low. If I wait longer - no problems firing her up. She fires up fine the next morning after parking it for the night.
I put it on my trickle charger the other day and when I checked in the morning it showed that the battery was fully charged. But today, same problems.

Any thoughts?

Thanks

I think so. I have the paperwork in my glovebox. But the Stang's at the shop getting my X-pipe installed. I pick it up tomorrow. I'll stop by Sears and have them test it.

Thanks

Thanks for the help. The battery was done.