Macbook early 2011 battery life

I have a Macbook Pro early 2011

 

And over the last 2 months my battery life has crapped itself. I used to get a good 3-4 hours with it just surfing the web and listening to music but now I can't even get an hour with it at the moment. No idea whats up?

 

I have lost 10% of my battery just spending 5 minutes looking through forums looking for an answer?

 

Thanks!

 

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Tim

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