Telenav Scout is the biggest drain on my Galaxy S2 battery of any app I've tried.
Even when I had my phone plugged into a charger and the battery was supposedly charging, Telenav Scout completely drained the battery after a couple of hours. Without the charger, it would completely drain the battery in 40 minutes or so.
On top of that, Telenav Scout so hogs the CPU that the phone started giving me high temperature alerts. The phone felt like it was catching fire. I had to shut it off to enable it to cool.