I have heard there is a possibiity the battery indicator circuit was uncalibrrated. If you keep your battery charged most of the time, the battery indicator circuit loses its accuracy over time. In this case, running the computer to a very low battery recalibrates the circuit and now it will be fine.
On the other hand, it sounds like this happened more than once, which more likely means the battery is shot. If you regularly run your lappy until your battery is very low, this is by far the most likely explaination. After 8 months, Sony is not likely to give you a new battery. But if you bought the extended service, you can give it a go.
The (least likely) third option is that there is something wrong with your motherboard, which would be a waranty repair.