Fitbit Sense 2 FB521 Fitness Tracker Battery Replacement
Over time the battery in your Fitbit Sense 2 will die battery will die more quickly. To get back to full-day battery life, replace the battery with a fresh one
Parts you'll need 🧰
If the tool cost seems prohibitive, check out our repair catalog to see if we offer repair services for your device. If it's not listed, we don't repair it.
- A replacement Battery
- Scroll on the product page to "Frequently bought together" to add all the tools you need as well.
- Or, select your battery below if you only need the part.
- Thin Pry Tool for screen removal.
- Rubbing Alcohol
- Nylon Spudger Tool (For unlocking ribbon connectors and doing other tasks that require a non conductive tool)
- Heat Gun (A hairdryer can also do the trick)
- Repair Kit (All the screwdrivers you'll need)
- Some 704 RTV
- Anti-Static Parts Organizer Mat
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1. Remove the Screen
1.1: Heat the screen with a heat gun set to 200°C (392°F) until the watch is warm to the touch. Make sure you move the heat gun around so as to heat the whole screen rather than just one spot.
If this repair seems daunting, check out our repair catalog to see if we offer repair services for your device. If it's not listed, we don't repair it.
1.2: Dip your thin metal pry tool in some 99% Isopropyl alchohol then carefully slide it between the edge of the screen glass and the metal housing. **Do not insert the pry tool more than a quarter of an inch or so as there are ribbon cables that you can damage.
1.3: Rock the pry tool back and forth the break up the adhesive then dip it in more alcohol and insert it on another side of the watch. On each side, end the rocking back and forth by pushing the pry tool down to apply a bit of upward pressure to the screen. Repeat these steps for all four sides.
1.4: With the button on the side of the watch facing upwards for orientation, insert your metal pry tool on the right side of the watch (it would be the top if you're wearing the watch) then bend the tool down to pull the screen up.
1.5: Once you've created a small gap between the screen and housing stick your fingernail in it to keep the gap while you then insert a slightly thicker pry tool into the gap. Use that pry tool to lift the screen, being very careful of the ribbon cables that connect the screen to the motherboard.
1.6: Remove the four screws, one in each corner then lift up the silver bracket that covers the screen connections.
1.7: Disconnect the ribbon cable by gently sliding your pry tool underneath the connector and lifting up. It should pop off of it's connector fairly easily.
2. Removing the Battery
2.1: Disconnect these two ribbon cables by carefully lifting the plastic locking flap with your nylon spudger.
2.2: Gently slide the small ribbon cable out of it's connector with your nylon spudger using the stiff nib that sticks off each side of the ribbon.
2.3: Lift the mainboard and battery assembly out of the watch using a flat head screwdriver to pry it up between the housing and the edge of the assembly shown in the first photo. Once it's free of the housing you can gently tug the larger ribbon cable out of its connector.
2.4: Remove these fours screws on the back of the assembly.
2.5: Open up the mainboard/battery assembly and use your nylon spudger to disconnect the ribbon cable connector from the mainboard then carefully lift the battery away from the assembly.
Pry from one spot then another and another to displace the pressure as you lift it. **Do not use a metal pry tool for this and be careful to not puncture the battery as it will become a fire hazard.
3. Installing the New Battery
3.1: Clip the new battery ribbon into its connector by lining up the plug to the socket then gently pressing down until it clamps into place.
3.2: Fold the battery down onto the main board as shown below then fold the assembly closed. If the new battery is not sticky, you can use some very thin double-sided tape to hold the battery in place. Press it down firmly to ensure it's secure.
3.3: Fold the assembly closed and reinstall the screw in each corner.
3.4: Line up the wider ribbon cable in the housing with its socket and slide it in then close the locking clip.
3.5: Before you lay the assembly down into the housing, make sure that the second ribbon cable is not trapped underneath the assembly and sticks outwards over the edge of the housing. Then lay the assembly down and use the pointed end of your nylon spudger to slide the ribbon cable into its connector. You can then close the latch to secure it in place.
3.6: Reinstall the these two screws
4. Reinstall the Screen
4.1: Connect the screen connector by lining up the plug with the socket and very gently pressing it down into place.
4.2: At this point, your watch should be working. Try turning it on by holdingdown the button for a few seconds. Test the touch and make sure the screen works properly. If it works, install the metal bracket and two screws that hold the screen connector in place.
4.3: Remove the old adhesive from the housing and the edge of the screen using your nylon spudger.
4.4: Apply a thin line of glue in a continuous line around the edge of the housing.
4.5: Press the screen down onto the housing and use a Q tip dipped in rubbing alcohol to clean off any excess glue.
4.6: Put the watch in a clamp or wrap it tightly in a rubber band for 24 hours to let the glue cure.