The shut off point is variable based on several factors. But it averages between 1% to 10% for shut off. It won't auto turn back on till it reaches 5%. So your well within the norm. As the phone learns where the top and bottom of the battery charge is, it can get closer to showing 1% before turning off. Currently my iPhone 4S shuts off at 4%, my wifes iPhone 4 shuts off at 2% and my daughters shuts off at 1% because she has run it dead a lot.