The week 5 secret battle star is located on the mountain between Salty Springs and Fatal Fields. Land on top of the mountain and head to the grass patch to collect the week 5 secret battle star.
You will need to unlock the week 5 loading screen first by completing the week 5 LTM missions.
Week 5 secret star map location
The exact map location of the week 5 secret star.
Head to the mountain in the map location above. You will see a patch in the grass where the star will be located once you unlock the loading screen.