MacBook Pro battery charge indicator completely wrong

I'm having some severe problems with the battery of my MacBook Pro since two or three weeks: the indicated charge and remaining battery life are completely wrong. Usually, the computer shuts down without any warning with a drained battery and an indicated charge between 30 and 50(!)%. About every second time, the MBP doesn't even just go into sleep mode, but completely shuts off. This has resulted more than once in a complete loss of my work.

I already have tried to recalibrate the battery more than once, resetted the PMU and installed the Battery Update - without the slightest success. The battery does not show any of the symptoms described in the read-me for the Battery Update, so it's not eligible for replacement. Is my battery defective?