Usually, I get asked how long the battery will last between charges. That is a fairly simple question to answer. As a matter-of-fact, Garmin answers this on their own website. For example, on the popular Forerunner 410, they tell you to expect 8 hours of battery life.
However, in real usage, that number is a variable, especially since satellites aren’t 100% predictable and the watch will sometimes lose a signal.
Regardless, the real question remains, how long will the battery last in my watch before I need to get a new one?
Properties of the Battery in my Garmin
First, let’s take a look at the battery itself. Garmin uses rechargeable lithium-ion batteries. There is a lot written about these types of batteries. For the average person, Wikipedia will tell you a lot on the Wikipedia rechargeable lithium-ion battery page.
Pay attention to cycles. Cycles are simply the number of times that you can fully recharge the battery before the battery cannot hold an acceptable charge. Wikipedia is very broad saying that the rechargeable li-on batteries can be cycled anywhere from 400 to 1200 times. Unfortunately, that’s a broad range, so we’ll have to make assumptions to narrow it down.
For simplicity, let’s say that the average life of the battery is 600. I use 600 cycles instead of splitting the range to 800 because most people don’t fully discharge their battery. Now that may be old information that you must fully discharge before recharging, but I would rather be conservative, which is why I selected 600 cycles as the useful lifespan for a runner.
Calculating Lifetime Battery Life
Now, how do we convert 600 cycles into something meaning for a runner? We need to estimate how many times a week the average person will recharge their Garmin Forerunner. Based on my inexact method of asking about 15 people, the number is between 2-3 times per week. Now, let’s make some calculations.
Our formula is: 600 cycles / number of charges per week = number of useful weeks
Years of Useful Life: 5.8
Low Number of Charges is 2 per Week: 600 / 2 = 300 weeks of charges (5.8 years)
Years of Useful Life: 4.6
Medium Number of Charges is 2.5 per Week: 600 / 2.5 = 250 weeks of charges (4.6 years)
Years of Useful Life: 3.8
High Number of Charges is 3 per Week: 600 / 3 = 200 weeks of charges (3.8 years)
As a final note, when considering buying a used Garmin, look at these numbers and compare to the age of the watch you are buying. If the watch is going on 4 years, it is probably smart to avoid buying that particular watch.