reply to batsona
Re: Troubleshooting fast batt-drain.... GPS only "activates" when an app requests it to. My GPS is always "on", or more like, "ready if needed". The GPS icon will appear in the status bar when it's actually working.
For WiFi, since you're driving, there's no use for WiFi as you'll never be in range of any access point long enough. Turn it off. You could adjust how often it scans for WiFi access points (basically it wakes up the WiFi interface looking for connections and notifies you if it finds any). The default interval varies wildly ! Mine is set at 360 seconds (6 minutes). If I have to, I can *force* it to re-scan if I go someplace with WiFi.
See if your device has a "sleep" mode or "nighttime" mode. It's like a pseudo-airplane mode. It generally dims the screen brightness, turns off data (WiFi, 3G/4G), but leaves cell data on so you can receive calls and text.