Garmin Fenix 5 Battery Replacement

This isn’t a full guide, but some helpful hints if your Garmin Fenix 5 battery has dropped in battery life and needs replacement. Be carefull when undertaking as if you mess some of this up you could break your expensive watch. It’s relatively easy to do but we live in a world where we have to tell people not to drink bleach so you know….

Officially it doesn’t seem Garmin want to do a battery replacement service, I suspect so they can sell you a new watch.

My Fenix 5 was advertised as around 18hrs in full GPS mode when new and was around that, maybe a tad shorter with navigation on. Of course you can use ultratrac mode to increase but accuracy is awful and it seems pointless buying a watch that can track pace, distance etc to such a high accuracy and then pick a mode that’s marginally more useful than a £5 Casio watch from the market.

Over use my Fenix 5 dropped to closer to 12hrs as battery life depleted.

For ultras this is annoying as you’re getting close to two charges over a 100 miler depending on battery life, how often you check it, and whether you’re able to charge it the morning of the race and have it 100% the moment you cross the start line.

For general use as an every day watch this also got annoying. What was a weekly charge depending on number of training runs dropped down to every few days and if going away for the weekend I needed to pack a charger or ensure it was 100% as I left home.

A few people had suggested changing the battery as they found some cheap replacements on eBay so I decided to have a go.

Easiest place to source is from eBay, and accept that postage will be expensive and take a while as either from China or Germany. In my case I paid £16.76 delivered and it took 8 days, far less than the 2-3 weeks quoted on the advert. When searching try to make sure you get a Fenix 5 not a Fenix 5X. The adverts are not always that clear. Some of the eBay ads have complete used rear assemblies including batteries from refurbed units in China. These would be a very easy swap but with no way of knowing how much better the battery life is you might end up with a worse one.

As you’ll see later, the quality of the batteries in terms of fit varies. If you can find one with an accurate photo and it looks closer to the original battery below it will make fitting easier. A lot of the ones supplied are a bit squarer without the corners rounded off so a little more effort to fit.

The complete replacements from eBay in China showing the slightly curved edges of original batteries.

Taking apart –

There’s lot of Youtube vidoes on this, I found this one good: https://youtu.be/2o_F6NxtkAk

For some reason they all seem to go through the front of the watch though, and need to remove the main board and the GPS antenna to get to the battery at the rear.

I went through the back – need to remove 4 screws and need a T5x50 driver (a very tiny Torx driver).

Four screws on rear

When taking apart you’ll notice the screws aren’t mega tight. They’re there to provide the appropriate compression on the rubber gasket to maintain water tightness so when reassembly don’t assume you need to use the force of ten tigers to do back up as you’ll either strip the threads or distort the case.

Once open you’ll see the battery on the rear, it’s attached by a sticky pad to the rear case. You can see the battery lead at top (blue arrow), take note that RED wire goes to terminal nearest edge. The battery connection is designed so you can’t plug it in the wrong way around but worth checking.

You can see gasket has become stuck to the rear case and will need swapping into the grove on the main body.

To disconnect the battery lead you might assume you pulled it along the circuit board, so broadly in direction of blue arrow, but actually you pull it up away from board (so towards you). Small tweezers may help with this. Once disconnected you need to gently prise it away from the sticky pad. Note it’s a battery and full of chemicals you’d rather not leak so use a spudger (plastic opening took) or a flat screwdriver VERY CAREFULLY and work your way around.

If during this step or any of the next you manage to disconnect the ribbon cable from the rear circuit board to main board (red arrow) then don’t worry. Once the battery is installed and ready to go this simply pushes back on if you line it up.

It’s probably worth at this point transfer the gasket from the rear case into the grove of the main body to ensure it sits properly. The gasket is broadly round with a flat section on side so use that to line it up.

To connect the new battery you put the plug on top of the board, ensuring red lead is nearest edge of board, and push it down onto the board. It won’t make an audible ‘snap’ at it locks into place but you should feel it slightly give as it slots in and become secure.

New battery connected, red cable nearest edge.

The new battery, although marked as Fenix 5 is not a 100% match. You’ll note the power cables are longer, and the battery is a little bit more rectangular (the one removed has the corners curved a little). It will fit but require some delicate insertion. The cables aren’t long enough to run them the length of the battery and have them exiting the battery on the opposite side of the connecter so need to lose some length as you assemble.

It was hard to get photos of the rest or process as fiddly to close up, keep pressure and install screws but with some persistence you will manage it.

It’s worth doing a couple of turns on each screw and making final check before screwing them fully in. DO NOT OVERTIGHTEN.

I didn’t get a photo of the new battery but the specs on the box were –

Li-Polymer 230mAh, 0.9Wh, 3.7V, labelled for Fenix 5, made by www.eco-gmbh.de

Old battery was part 361-00097-00 and specs –

Li-ion 255mAh, 0.97Wh, 3.8V and dated 01/08/2018 which is about two months before I purchased the watch.

So new battery is slightly smaller capacity – time will tell on what life I get. A lot of the adverts are a little vague on exact delivered spec. Worth noting that according to internet (so it must be true) “The key difference between lithium ion and lithium polymer is that lithium-ion batteries have a high energy density, whereas lithium polymer batteries have a low energy density”. Li-po are often used now for safety and lighter per Wh capacity so where space less of an issue, can actually weigh less even though physically larger.

I tested the watch with new battery on normal GPS mode and it died at 17h50min, pretty much same as it got when new, maybe a fraction less.

Important point – when you reassemble it all, close it up and do the screws up, don’t triumphantly turn the watch around, see the dead screen and swear loudly that you’ve broken it! The watch is off. You need to turn it on using the button in usual way. I heard someone do that. It was me. Idiot.