Battery discharging

I've been having problems with the battery lately.  The cold weather sucks the juice out of the battery faster than anything I've seen before.  Nowadays, even in the underground garage, I would have problem starting the bike and often than not, the battery would die in the process.  I've taken the bike out to Mississauga (30km away) over last weekend, and left the bike in the cold at -10C for about 5 hours, and it barely had any juice left to start the bike.

So, after I got home this past weekend, I took the battery out and thought I'd hook it up to the battery tender to trickle charge it.  Then, I thought maybe I'd capture the discharge rate of the battery first.

At the beginning, when I first brought the battery to my apartment, the battery was still cold from the ride.  The voltage dropped by 0.1V in about 3 hours.  Then, the discharge quickly settled down to 0.05V per day.  I'm not sure what this means yet.  Does the battery need to be replaced?  Well, before I connect the battery tender up, I'll take the battery back down to the bike and see if I could start the bike up.  I'll do a test with the cold as well, leaving the battery out in the cold and see how fast the discharge is.