Battery died in my Tag, these are the tools needed to replace the battery. You can get a watch case opener on eBay really cheap and I used my bench grinder to grind down a center punch
Start by opening the band. They have spring pins that pop out easily, just make sure to keep your finger over it when you remove it so it doesn't fly away from you.
Take your watch wrench tool and adjust the teeth to fit the grooves in the back of the watch
Apply pressure then turn the wrench left, while holding the watch with your other hand
Once the case is off, see how the battery is being held in place. Every watch is different, but its usually tension or a small screw that will hold it in.
Once I pulled the bracket holding the batt down, it popped up
Replace with the same type (google the numbers on the battery)
Case back on, and tighten
Set the time and date, and you're good to go.
- Watch case wrench
- Small screwdriver
- Center punch