Misdiagnosis/No warranty

6 months ago I booked my car for a major service at the abovementioned, I was told my car battery is faulty, even though I tried to explain that the car hasn't given me any problems or indicated that the battery is faulty, they INSISTED I get a new battery. Motor plan authorised and the NEW battery was put in. Last Saturday the car had problems to start, it made a \cranking' sound a couple of times before getting into ignition. I immediately booked it for diagnosis and repair. To my biggest surprise I was told my 6 mths-old-battery IS FAULTY"I told them that's impossible as they replaced my battery a mere 6mths ago. They INSISTED it's the battery and I had to pay for it this time as my Car Warranty plan wouldn't pay for it. When I asked about the warranty of this 6-months-old battery"