My latest little project has been replacing the battery in our Garmin GPS.

We have been using this Garmin GPSMAP 276C since 2003 and although it is old we haven’ t found one that has functions that we like any better.  The main things we like are that it is waterproof so we can use it on the motorcycle as well as the boat.  It also has a Marine mode so we can use the Lakes & Rivers maps in it when we are boating.

All good stuff *except* that it uses an extremely tiny internal battery to keep the clock running when the unit is shut down.  This allows the unit to find the satellites quickly when it is powered up because it knows  where to look for particular satellites in the constellation.  Without the current time it has to just start a blind search and when it does stumble onto a satellite it has to then download the almanac and synchronize  its clock with the GPS time.  This process can take anywhere up to 10 or 15 minutes.

As you might guess that little (rechargeable) Li-Ion battery stopped holding a sufficient charge a couple of years ago.  When I did a search on this model of GPS I got lots of hits about that battery giving out and that if you have Garmin replace it there is a flat charge of $200.   I refuse to  pay Garmin $200 to replace a battery but fortunately I also saw where other guys had replaced the battery by themselves so I decided to give it a try.

I first ordered the battery from DigiKey.  The battery was only a couple  of bucks but they called and said they weren’t allowed to ship it through the Post Office and that UPS Ground was going to cost $18.  I cancelled the order and did a bit more searching.  I found that a similar battery on eBay was available from China.  I ordered two batteries figuring I might damage one trying to solder it in place.  I got them in less than two weeks for $9.00 (including shipping), and best of all the package arrived by US Postal Service right in my mailbox!

So I proceeded to tear the GPS apart.

Garmin GPS opening unit

Opening the Garmin GPS unit

Doing the tear-down was a little scary.

Garmin GPS repair

Lifting screen off board

Two of the screws that held the main board in place are inside this foil covered compartment.

Garmin GPS repair

Peeling back the foil

I had to tear open the foil shield to get to the screws that hold the main board in place.  The battery is on the back of the main board so the entire main board has to come out.  I replaced this foil with aluminum tape.  Didn’t look as nice but  I think it will keep the computer compartment shielded from the RF stuff.

Garmin GPS battery

Turn board over and there is the old battery

This is the culprit.  It is *really* small, that is my little finger in the pic.  I think the battery is 5mm in diameter and those leads are super tiny.

Garmin GPS battery

Replacing the old battery with the new battery

I got the old battery off without destroying the resistor that is mounted right beside the positive lead.  I tinned the leads, used lots of flux and held the new battery in place with  some tape while I just dabbed the leads with the tip of my smallest soldering iron.  Not  as smooth as the original solder flow but it seemed to be reasonably secure.  Some guys  on the Web said that it was too difficult to solder so they used “conductive glue” to attach  the new battery.  I had never heard of that stuff but decided to give the soldering a try.

The old 3.6V battery was only measuring 0.9V after lots of charging, no wonder the clock wouldn’t run when the unit was shut down.

Amazingly enough, when I put it all back together it worked!   So I managed to fix the GPS for $9.00 and I have a spare battery.  Hopefully I’ll get another 10 years out of this one.