Some lenovo laptops may have defective batteries:

The issue affects ThinkPar R60, R61, T60, T61, X60 and X61 machines sold worldwide. It manifests itself as a sudden drop in the battery charge displayed by Windows or by a very short battery life.
You can download a testing tool here:

They will replace the defective ones free of charge.

N.B. This is NOT a safety issue, it just affects performance.