How to Replace Battery in Garmin Forerunner 405

The Garmin Forerunner 405 is a classic GPS watch by Garmin. You can find many of them available for sale on eBay for a steal. The great thing about old GPS watches like the Garmin 405 is that they still track GPS just as well as the new ones. The only thing that has been added to improve tracking accuracy is the GLONASS integration on a limited selection of GPS watches.

So how do you change the battery on a Garmin 405? It’s easier than it looks but it requires some basic soldering skills, please proceed at your own risk. Here is a layout of the tools that I used and suggest using:

Weller WLC100 Soldering Iron
T5 Screw Driver
Flat head screw driver
solder
solder wick
Helping Hands (not in picture below, but used)
New Battery for 405 (not in picture below, but used)

1. Start by flipping the Garmin 405 over and removing the 4 rear screws with a Torx 5 (T5) screw driver.

2. Once the back is unscrewed do not pull it off immediately as there is still a connector attached that you will want to use the flat head screwdriver or a spudger to remove. Disconnect carefully and separate the back from the watch.

3. After the back is separated, carefully remove all the tape and stickers. You will also want to remove the battery which has a sticky type of glue from the rear plastic housing.

4. Now you need to remove the old battery with your soldering iron and soldering wick. Touch the two contacts with the soldering iron, once the solder is wet, use the wick to absorb it and then separate the batteries connecting tab.

5. Now you will start reversing the process. Take the new battery you have purchased and bend the tabs so that they will neatly wrap around the circuit board as the other batteries tabs had. **Important Note – as you can see on your circuit board there is a negative and a positive connection. Look at your battery to see which side is which before soldering on.** Then, with the help of the helping hands or real helping hands, solder the new battery onto the board. My solder connections here were very neat or clean but the important part is to not glob on too much solder and have a clean connection.

6. Attach the stickers to the battery and the battery to the watch case rear housing. If the glue stayed on your battery and not the case don’t worry – it is snug inside of there and doesn’t require glue but you can use double sided tape if you’d like.

7. Carefully reconnect the connector to the main watch body and screw your 4 torx screws back into place. That’s it! Charge it up and go for a run!

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Dario

Dario is a long time distance runner and OCR athlete. When not on the roads and trails logging miles he can be found drinking coffee while reading bad science fiction books.

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