Battery life will vary greatly depending on how often you use the application. The main functions which will drain the battery are screen utilization and GPS. The performance should be similar to that which you can expect using any other tracking app.
We have found that adding a protective case to your phone increases insulation and improves battery longevity. Also, bringing a powerbank (an external battery charger) for those longer trips will help.
In terms of safety, when venturing outside of marked runs or adventurous terrain, you should always carry a paper map and compass.