I use Waze on a Nokia Lumia 820 and the battery drain is a problem, indeed.
As a workaround, I set my phone to use 2G connection only. 3G and 4G/LTE internet connection draws much more power, not only with Waze. In my experience a 2G connection is enough to update all infos in the app, as it generates quite low data traffic. With this setup, the fully charged 1650 mAh battery of the Lumia 820 is enough for about 1.5 hours of navigation. If I use my 890 mA car charger, the battery drain is very small, a few percentage points per hour. So with this workaround and a car charger, Waze is ok for even longer trips. But I still hope the app can be fine-tuned to draw less power.
Krisztian from Budapest / Hungary