Ultra Stretching the Garmin Forerunner Battery Life
Getting the most juice out of a Forerunner watch for an ultra marathon event
In my ongoing love/hate relationship with my sports watch I've learned a few tricks to help improve the battery life of a Garmin Forerunner model. I have the 945 edition, however this advice should apply to a few of their Forerunner models.
When talking about any event under 6 hours you needn't worry about whether the watch will last the whole activity, a full charge beforehand should give you plenty of juice to last to the end of the event.
However when stretching to longer events like ultra marathons, battery life becomes a serious consideration. Whilst Garmin advertise up to 30 hours activity tracking from a single charge, in my experience it's closer to 10 hours on the default settings out of the box.
This article will go into how you can configure your watch to stretch that battery so you can track 10+ hour events and gather those sweet sweet run stats.
Bluetooth and Wi-Fi
First things first, turn off Bluetooth and Wi-Fi during the event. To do this go to the controls menu (hold the top left button on the watch) and disable the phone and wi-fi connections.
These only drain a small amount but it is noticeable over longer distances.
The default backlight config can be a substantial drain on the battery. Out of the box the backlight with turn on for 8 seconds whenever you switch to another screen or receive an alert, at all times, and use a relatively bright setting. It will also turn the light on by gesture (flicking your wrist to view the watch) when it's dark.
To change this to a more energy saving profile do the following:
- On the Watch Menu go to -> System -> Backlight
- During Activity:
- -- Set Keys and Alerts to After Sunset
- -- Set Gesture to After Sunset
- -- Set Timeout to 8 Seconds
- -- Set Brightness to 5%
This way the backlight will always be off until the sun goes down, you can still press the top left button mid activity to turn the backlight on for 8 seconds if you wish (maybe you're running through a tunnel!) though in daylight the screen is often plenty bright enough alone.
Switch to GPS Only Mode
By default a Forerunner 945 comes with GPS + GLONASS enabled; this system tracks 2 satellite networks to better triangulate your position. The idea is that if you lose signal to the satellite, or are under heavy cover (like a forest or a city with high rise towers) then this mode is better for re-establishing your position.
It is also hungrier on battery life than the GPS Only mode. In practise I've found both to give almost identical levels of accuracy in terms of positioning and picking up the network, whilst I tend to find the battery usage for GPS + GLONASS is around 30% more than GPS Only.
For an ultra I'd highly recommend switching to GPS Only mode by:
- Go to Activities & Apps -> Your Run Profile -> Run Settings -> GPS
- Set it to GPS Only mode
Note: it's important you sync your watch with Wi-Fi or sync using the Garmin Connect app on a laptop frequently as this updates a file on the watch called a "CPE". This is what the watch uses to predict where a satellite is, if it's out of date your GPS tracker will start losing your position frequently and take much longer to find the network.
You can check if the CPE file is up to date by going to Settings -> System -> About then scrolling through the pages until you see "CPE: Current"
Maps Display During Race
Now the watch is configured, a note on screens during the race. One of the Forerunner 945's most useful features is the Map screen, where you can add the GPX track of your route and use it for navigation. It is one of the main reasons I use this watch in the first place!
However be aware that, because the map screen requires the watch to update it's display frequently, it has an impact on the battery life too. For long races I'd recommend only switching to the map screen when you need to refer to it, then switching back to one of the other displays (like the pace display, or current time screen).
When In Doubt; Power Bank
A good bit of news is that the Garmin Forerunner's can be charged whilst still tracking an activity. If you are concerned it may not last the full length of the event, bring a power bank and the Garmin charging cable with you and give it a top up at aid stations, or even on the move.
Only thing to note is, as the connector is on the bottom of the watch, you won't be able to track heart rate during the charging.