Why is my battery life so short?

Unfortunately, this can happen from many things. The device being charged to often, the device being left in the heat for too long, the device getting moisture in it, the batteries power has decreased with time, etc. I would try resetting the device to factory settings, you may have certain apps or settings applied that take more battery to function. If resting the device does not change the batteries tendencies in the next few days, it is probably time to change the devices battery.