MBP with almost full battery switches off if Magsafe removed.

I have an older MacbookPro (2.16ghz Intel Core, 17") . Its started behaving bizzarely today - with Magsafe connected, its shwoing a green light, and the battery is showing as 91% full, and not charging.

Checking the health settings on System Info shows its in pretty good shape.

The instant i remove the Magsafe connector, the Mac shuts off. No warning, just instant shut off.

I have reset the SMU following apples procedure of removing battery and power, holding power button for 5 secs before reconnecting everything and rebooting.

Nothing seems to have changed - the battery still refuses to charge and the Mac dies if the magsafe is removed.

Any ideas what the problem could be?

or how to cure it?

thanks