Battery-MacBook Air

My battery life has dramatically fallen. I have had my macbook air for around two months. I currently have 85% battery and this leaves me with 1h35m.

When perchasing this lap top I paid in agreement that I was getting a 5hour battery life with my laptop. Why has this changed so significantly? I am truely up-set about spending over a £1000 for a laptop that seems to be falling under pressure and stress after only two months of having the product. This all seems like I have been lied to and bribed into buying a product that isnt what it said it was.

unhappy customer

Gordon