I love my Garmin Forerunner 305. It was the first running watch I purchased in 2010. Much to my dismay, after three years of use, the battery began to die after only an hour of use.

Frankly, I didn’t have the money to replace it. Since I also love a good DIY project, I took a shot at opening it up to see what was inside and found a very inexpensive way to fix it and replace the battery on my Garmin Forerunner 305.

Tools you’ll need:

  1. New Battery from Amazon (around $10)
  2. Soldering Iron
  3. Solder
  4. Wire Cutters
  5. Gorilla Glue (or some type of really strong adhesive)
  6. Electrical Tape or zip ties.
  7. Box Cutter/knife


Watch the video below for the complete explanation and walkthrough of the process.

Basic text walkthrough.

  1. Use the utility knife to cut away the rubber on the outside of the watch. You’ll use the sharp edge to cut carefully inside the grooves.
  2. Once the unit begins to open, use the knife to CAREFULLY separate the two pieces AT THE BOTTOM (near where it says GARMIN). DO NOT SEPARATE FROM THE TOP. The main board is there and you will damage the watch.
  3. Once the 305 is in two pieces, use the wire cutters to snip the wire from the battery to the unit.
  4. Remove the old battery.
  5. If you purchased the battery from Amazon, cut off the white wire (you don’t need it). And use the wire cutters to strip the ends of the wire to bare copper.
  6. Hook the two wires together and use the soldering iron and solder to join the two wires together.
  7. Now it’s time to test. Put the unit back together by pressing down on the top unit, and plug into the wall. At this point, the battery should display the unit as charging.
  8. Use the Gorilla Glue to glue the battery to the plastic part of the unit. You may have to snip down a few small plastic pieces on the bottom of the unit so the battery fits in. Give the battery time to sit and dry.
  9. Attach the two pieces of the unit together and use the silicone to put a thin layer of adhesive between the two pieces.
  10. Bind the GPS together with electrical tape or zip ties and let dry for 24 hours.
  11. Voila! Brand new Garmin 305 🙂
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