Step 1: Triangle File
Purchase a small triangle file $1 fr hardware store
Step 2: Check Fit
Compare if fits snugly into the triangle screw head
Step 3: Remove Screw
Unscrew normally. Can use a plier to increase the torque as it can be quite tight
Step 4: Repair Battery
Refer to another Instructables for changing out the defective cell inside the battery pack.