[V12Bill]

I had this problem with my Battery Tender and asked the Battery Tender agent at Carlisle about it. He called tech support and we were told that you should unplug the transformer from the A/C outlet before you disconnect the clamps from the battery. It seems that if the transformer is not unplugged first, then when you reconnect the clamps the transformer does not "recognize" the battery and stays in the red or charge mode.
Disconnect the transformer first when disconnecting from the battery and plug it in last when hooking back up. I started doing this and the red light goes out sooner. Hopefully it will "recognize" the battery sooner and the red light will not come on at all.