Hi yes I think it is. I have two 2008's and both batteries needed replacing within two months of each other.
On the 08 S, it started to take longer to crank before starting till finally left me in need of a boost (about 3 weeks passed), where I then went to my local Nissan dealership and got a Nissan battery. Replaced it myself and its been fine since.
On the 08 SL, had an oil/filter change done and the Nissan dealership also does a multi point inspection, including battery charge test. The battery in this car failed the charge test so I did the same thing as the other car. Dealer service mechanic told me typical life is 3 to 4 years on the stock battery so if you are getting more than that, that is great.
Based on your comments and my past experience, I would recommend a new battery if it is taking longer to start than normal and/or it fails a charge/load test.
Hope this info helps.