Originally Posted by br3nt
You may want to try using it with airplane mode turned on. If the nav app you're using downloads the chart to the phone, it may be able to use GPS without enabling data. Also it may save your battery over using Bluetooth but I can't say for sure. I don't know what the consumption difference is between BT and GPS.
On my iPad I turn off WiFi and 3G, which I guess is the same as putting it in Airplane mode. I guess I can save a step and just do that next time.
I do it because the battery lasts longer, but I suppose it saves data too. I never run over on my iPad so I didn't give that much thought.