Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Batteries didn't last

I purchased this battery pack back in 2009, and two years later I am already looking for replacements. On a full charge the display indicates 36 minutes remaining, but it typically dies after one or two uses. The run time is getting shorter and shorter. I've had to plug it in to finish my shave. I'm hesitant to buy these batteries again.