Given reviews from Amazon, classify those review based on their content into two classes: Negative or Positive.

Let me give you an example: I've read this book with much expectation, it was very boring all through out the book
The answer to this example can be: Negative
Here is why: Review writer does not like the book because it was boring, therefore it is a negative review.

OK. solve this:
The battery I got has a terrible quality. With a full charge over night (~8 hours), the battery only sustained my SD800 IS camera less than 12 hours normal usage, shot around 20 pictures. Versus to the original battery pack with the camera, the original battery can last over two days normal usage, shot around > 100 pictures. I believe the vendor selling degraded products.
Answer:
Negative