Hey Mark05, I think I had the exact same issue as you! My charger flickered from green to amber every like 15-45 secs. The battery would still charge, but I confirmed that I had a problem when I started noticing that after unplugging the adapter, the computer would inevitably shutdown within 10-20 minutes even if the battery was fully charged.
Your solution is to call apple care and explain your situation. They will send you a replacement battery. I have an applestore near me, and I went there and they replaced it on the spot. If you go to the applestore though, make sure you schedule an appointment via
http://www.concierge.apple.com .
Whether or not your mac shuts down without the adapter, you should probably be noticing that the battery life of your MBP is pretty much shot. That was the case with mine, even though I wasn't able to appreciably notice the difference until my battery was replaced. I now get 1-2 hrs more per charge!
Basically, the "genius" at the applestore told me that my battery was dysfunctionally taking up charge.
Good Luck with everything
hope my experiences help you in your quest to fix your MBP.
