Sick Battery?

On Labor Day I put 200 miles on my motorcycle riding from my house, to Zimmerman, to my house, to my brother's house, to Hastings, to my sister's house and home again.  It was a beautiful day for a ride and I had absolutely no trouble.  Plus I got to ride in a group of five which is always fun.  One of the members of the riding group had a battery that would not seem to hold a charge. Once his bike was turned off it would not start again without a push start.  It is no easy task to push a big Harley with a big guy on it fast enough to start it.  Whatever his problem was, I believe it might be contagious.  Possibly Deadbatteryitis.   The next day when I went to go to work on my bike, it was very slow to start.  I got it going finally and it started fine after work and again after working out at the gym.  But the next day and every subsequent day, it will not start. I've had the trickle charger on it and it will try to start for a few seconds and then click, click, click, click.  A friend tested the battery and it came out as 12.5 volts which should be enough to start it. The battery is 3 years old and that is about the lifespan of a motorcycle battery.  I could replace it but I am not sure that is the problem.  I talked it over with a local motorcycle repair shop that I trust.  They suggested I bring the battery in for them to test.  Even if it shows 12.5 volts on a voltmeter, that does not mean it doesn't have a short in it.  I can remove the battery myself and bring it in.  I hope that the battery is the problem and my motorcycle does not need an ambulance ride.  And I'm grateful it broke down in my garage and not out on the road somewhere.  I hate being stranded.