New battery is not charging. Magsafe light turns green / orange

Just replaced the battery (easy - great kit! from IFixIt). However, after powering my computer back up I noticed the magsafe light going from orange to green, then to orange… repeats endlessly. System Information says the battery is not charging.

I tried resetting PRAM and SMC, but I keep getting the same problem. I opened the computer again, disconnected the battery, connected it again, same problem… tried resetting PRAM and SMC again… the problem wouldn’t go away. Installed my old battery and the thing runs Ok (only runs out of battery in about 2 hours).

I’m quite disappointed. It seems I just threw my money away.