Basically my Maps app on my iPhone 4S (with the latest iOS update) will not give turn-by-turn voice navigation if my phone is plugged into the USB charger on my car. I recently started a job which requires a lot of driving and I would really love to get the voice navigation working. My phone is older and the battery drains very quickly so it's necessary that it be plugged in during my trips to charge. The voice navigation works fine when my phone is not plugged in. Are there any work arounds for this issue?