Lenovo — Low battery backup

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Bareilly, Uttar Pradesh, 243001

Lenovo is claiming battery back up of "thinkpad x1 cabon" up to 11 hrs however at some sites its 9 hrs and suprisely in usa 8 hrs. But in actual backup is only 3-4 hrs. I have compaint in march and they change the battery in 5th of may 2016 but still problem the same. I again drop the mail to customer care but they people saying that 11 hrs is standered. But my argument is - whether this differnce 11 hrs and 3 hrs is acceptable.