iphone dying at 39% and fast

My iPhone is dying so fast and it'll die at 39% im running ios 7.1.2 and only have instagram twitter and ebay. and 2 games that only take up around 50mb each and i rarely use them. (once per week) i charge my phone at night and i wake up at 100% (7am) and itll be dead at 39% (at around noon) with only 2 hours of usage and 5 of standbye with no use of lte or it dies quicker. i only use wifi due to it dying faster with use of lte.😟