Garmin Body Battery: How Does It Work? Everything You Need to Know

If you’re comparing different Garmin watches and trying to choose the one that fits your needs, chances are you’ve heard about Garmin Body Battery Energy Monitor.

It’s a new feature that’s been implemented on some of its newer model watches – like the the Garmin Vivoactive 4 and the Garmin Forerunner 255. It’s designed to help you understand how well rested you are – or aren’t.

So what is Garmin Body Battery? How does it work and is it even accurate? Keep reading and I’ll tell you everything you need to know.

What Is Garmin Body Battery Energy Monitor?

Garmin Body Battery Energy Monitor is new feature on some of Garmin’s watches that combines a variety of metrics to estimate your energy reserve throughout the day.

If you’re well rested, your body battery will increase until it hits 100. If you don’t take time to rest, or if your rest isn’t actually restful, you’ll bottom out at 5.

Unlike science fiction movies, you’ll never actually hit zero – and nothing horrible happens to you if you hit 5.

But the general idea is that you’ll want to make sure your body battery is high before you start a strenuous workout. This indicates that you’re well rested and ready to give it your all.

If, on the other hand, your body battery is consistently low, you may want to think about why that is and make some adjustments to your daily routine.

How Is Body Battery Calculated?

Your Garmin device already collects data about your heart rate and activity throughout the day. Your heart rate variability (HRV), activity levels, stress levels, and sleep data are combined to estimate your body battery.

It’s best to think of Body Battery as a cumulative thing. This data won’t tell you anything about a single moment in time. But tracking them over the course of a day – or multiple days – you can estimate how rested you are.

if you have a restful night’s sleep, you should expect your body battery to charge over night and be high in the morning. If you have a calm, restful day, you should find that it’s still high at the end of the day.

On the other hand, if you have a really active or stressful day, your body battery will drain over the course of the day and be low. If you top that off with a poor night of sleep, you may well wake up and find your body battery still drained.

This can seem a bit counterintuitive at first, until you understand more about how physiological stress is defined and measured by your Garmin running watch. In fact, one of the best things about this feature is that it will help you better understand your body – and how it responds to different things.

You can read more about how Body Battery is calculated on Garmin’s support page here.

How Does Garmin Define and Track Stress?

Newer Garmin devices track your stress levels throughout the day, and that’s primarily what drives your body battery. People often misunderstand what this “stress” measurement means, and that can lead people to doubt or misunderstand the Body Battery feature as well.

Garmin measures physiological stress – not mental stress. Sometimes mental stress can have a physiological effect on your body, but not always. At the same time, your body can sometimes be experiencing physical stress and you might not otherwise notice.

This stress level is estimated and measured through heart rate variability – the variability in the amount of time between heart beats. When you’re truly at rest, your heart rate will be low and your heart rate variability will be high. Conversely, when your body is under stress, your heart rate will be elevated and your heart rate variability will be lower.

How does this work in action?

Let’s say you have a glass of wine with dinner, and then another couple of glasses afterwards. As your body processes the alcohol, you’ll notice that your stress levels increase. If this happens to be right before bed, you’ll notice that your stress levels stay elevated through the early hours of your sleep – and you won’t really “rest” until these levels return to normal.

Or, let’s say you go out for a run. Afterwards, as your body starts the recovery process, your stress levels will be high. If it’s an easy run, your stress level might return to normal within an hour or so. If it’s a particularly difficult run, especially a long run, it may be quite a while before they return to normal. After a long race, I usually find that my stress levels are elevated until late in the day, regardless of how much I rest the rest of the day.

Examples of Garmin Body Battery in Action

I’ve had a Garmin Forerunner 245 and had access to Garmin Body Battery since June 2020. At first, I didn’t quite understand it. But over the last few months, I’ve noticed several patterns now and I understand it much better.

As an example, let’s take a look at my own body battery on a typical Sunday.

At the beginning of the day (midnight), my body battery started out quite low. Saturday had been an active day, and I went to sleep kind of late.

I also had a couple of drinks before bed, and you can see how my stress levels were slightly elevated early on. As a result, my Body Battery charged slowly and it didn’t reach 100 before I woke up at 8:30. Nonetheless, I was fairly well rested when I woke up.

I then went for my weekly long run – about ten miles. I came home and rested up a bit, but my stress levels remained elevated for a few hours. Things returned to normal later in the evening and my body battery charged a little bit. I was active later in the evening, cooking dinner, and my Body Battery remained more or less level for the rest of the day. I ended the day above 50, which put me in a great position to rest up to full overnight.

Compare this to an average Monday.

You see a spike in my stress levels overnight. This was likely from a nightcap or two. You should be noticing a trend, whereby late night drinking has a pretty significant impact on your Body Battery. In this case, my Body Battery actually went down a little while I was sleep.

But otherwise, Monday was a very restful day. It’s typically one of my off days, and so I slept in a little later and I didn’t go for a run. I probably got up and walked the dog, and there are a few short spurts of activity.

The rest of the day was probably spent sitting in front of my computer working. I woke up with a my Body Battery almost full, and it stayed that way throughout the day.

Let’s compare this to one final example.

Now this definitely looks different.

The morning looked fine, and I got up and went for my morning run. But afterwards, my stress levels were high. This wasn’t a particularly strenuous run, so I was surprised when they were still high later in the day.

As the day went on, I noticed I wasn’t feeling great. I had some sinus congestion and a headache. I was legitimately sick for the next day or two. And if you saw my Body Battery for those days, you’d see that it bottomed out for a full day. It’s typical when you’re sick for your stress levels to remain elevated and for your Body Battery to charge little, if at all.

This is a great example of how the stress levels and Body Battery capture what’s really going on in your body.

Is Body Battery Accurate?

At first, your stress levels may seem a bit quirky. And who’s to say whether it’s reliably accurate 100% of the time.

But I’ve had access to this feature for the past few years, and over time I’d definitely say it is accurate. If I have a few days in a row where I’m not resting enough, I’ll notice that my body battery is low. Conversely, if I spent a lot of time being inactive, I’ll notice it stays high.

It’s best understood and utilized in this cumulative sense. You can use it to take stock of your daily routine and make sure that you’re getting enough rest. If you wake up every morning, and your body battery is low, something is definitely wrong.

What Makes Your Body Battery Go Down?

To give you a better idea of what influences your stress levels and body battery, here’s what I’ve learned through experience.

First, activity makes it go down. This perhaps goes without saying, but if you go for a run or a bike ride, you’ll see a drop over the course of that activity. More strenuous activities will make it drop more than relatively easy activities.

But it’s not just the activity itself. Post-activity, your stress levels may remain high and continue to drain your body battery. This is especially true after sustained, high intensity workouts.

Alcohol will have an impact. One or two drinks usually doesn’t make a significant difference. But if I have three or more drinks, I’ll definitely notice. It’s rare that I have more than four or five drinks, but after the occasional party I’ll notice that my body battery is depressed, and that it hasn’t increased very much over night. Here’s a good example of a Body Battery graph after a late night drinking.

Eating can also have an impact. After a meal, your body will digest your food. If you have a really big meal – in other words, if you over eat – you could see a sustained increase in your stress levels for a while.

Being sick definitely has an impact. If you’re legitimately sick, your stress levels will be elevated all day. It’s kind of freaky to look at the graph, to be honest. I wouldn’t want to see it, if I was sick for an extended period of time with something like the flu.

Coffee and caffeine will sometimes have an impact, too. I’m a heavy coffee drinker, and rarely will a day go by that I don’t have at least three cups of coffee in a day. It’s usually spaced out, but sometimes I drink a few cups in rapid succession. The caffeine will hit and I’ll feel a little jittery – and sure enough my Garmin stress levels will be increased as well.

What Garmin Running Watches Have Body Battery?

This is a relatively new feature, introduced in 2018. Older Garmin watches don’t have all the hardware necessary to calculate and track Body Battery.

If you’re looking at the Garmin Forerunner line, it appeared with the Garmin Forerunner 45, 245, 745, and 945. You’ll also find Garmin Body Battery on the latest generation (55, 255, and 955). This can be a reason to choose a newer Garmin, like the Forerunner 245 or 255, over the older 235.

If you’re looking at the Vivoactive line, the Garmin Vivoactive 4 and 4s are compatible with Body Battery. This can be a reason to choose the Garmin Vivoactive 4 over the older 3.

You can also get access to body battery with the Garmin Venu, Instinct, or Fenix 6 series.

What Do You Think About Garmin Body Battery?

Ultimately, Garmin Body Battery has reminded me of a few fundamental life tips – get enough sleep, eat and drink in moderation, and exercise enough but not too much. If any of those things get out of wack, your Body Battery will get out of wack as well.

How has your experience been with Garmin’s Body Battery Energy Monitor?

Do you find it useful or accurate? Leave a comment below.