unfortunately the generators do not show up on the maps, they do however only spawn in specific rooms, Armory, sec. hub, offices, and a few others. to avoid running out of battery look for batteries, they are small cylinders with a light on them, you can pickup and then use them to restore your light. hope this helps! side note: you may not be playing on the new version, the new version has tweaks made to the battery and flashlight which allow you to use it at a diminished capacity even with no battery, id suggest updating if you continue to have trouble.