Mini DV Camcorder Battery

I have two Lithium Ion batteries (Sony model # NP-FS11 and NP-FS11) and they are starting to go bad lately - after only about 6 months of use. The original NP-FS11 battery that came with the camcorder went completely dead after about a year.
For example, I can see "60 minutes" remaining on the camcorder on-screen and the next minutes the low battery indicator will start flashing and in another minute the camcorder will go to shut down mode. I do understand that a 120 minutes battery will not last 120 minutes but it should last at least 60 minutes. In my case, it only lasted 10 minutes.
When I measured the voltage across the terminals for both batteries, they both showed about the rated voltage, 3.6V. I did not measured the current though. I believe the charger (AC-VF10) is working properly.
Since these Lithium Ion batteries are pretty expensive and I don't want to have to replace them every six months, I was wondering if anybody has this same problem (& the solution) and did anybody contacted Sony about this already. I have been trying to find out if Sony has put out any service bulletin about this batteries but no luck so far.