Battery discharge issue

[drs]

I have an X61 with an odd battery issue. When it gets to about 40% charge, it suddenly jumps down to 4% and warns me it is about to shut down. When I plug it in, it takes as long to recharge from 4% to 40% as it does from 44% to 80%.

Cycle count is 39, and otherwise the battery seems to work fine. I bought the computer used. When I got it the cycle count was about 10, and it did it then, too. Any ideas?

[Harryc]

Sure, the battery is defective.