How much do you let the battery go down by before recharging?

I found this quite interesting.  It doesn't say what percent to start and stop charging, but it recommends periodically to discharge the battery completely. 

Pro-Tip: After every 30 charges, allow your lithium based battery to completely discharge before recharging. This helps to avoid a condition called digital memory. Digital memory can mess with the accuracy of the power gauge of the device you’re using. By allowing it to discharge completely you will allow the power gauge to reset.

This seems to support both arguments about when and how to charge if used in conjunction. 

RonHi said:

To be honest, I think this could be a valuable contribution to the discussion but I am not sure that I understand what you are saying this can teach us.

It is a pretty old watch and 400mAh is quite a good battery capacity. So probably you don't have to care too much about it

No memory issue w lithium ion.  You are thinking old Ni-Cad

Yes, it is best to charge lithium-ion batteries from 40 to 80 percent.

Manufacturers that use these types of batteries in their products know this too

For all we know they could be charging it using a method similar to the 40/80 rule in the background

You'll have to explain that to me in more detail. That Garmin loads the watch up to real 100%, you can see if you go into the service menu. The battery is charged to 4.35V. And that corresponds to the final charge voltage of a 3.8V battery as it is installed.
Garmin does not do 40-80 magic there. The battery is fully charged. Just as you want it.
There is simply no 40-80 magic of the manufacturers. And there is no manufacturer yet able to eliminate these chemical processes that negatively affect the battery below 40% and above 80%. Of course, manufacturers know how a battery works. But I am curious what you mean how they should solve it ;)

For all we know they could be charging it using a method similar to the 40/80 rule in the background

No, that is wishful thinking

gregjohnson1956 said:

You are thinking old Ni-Cad

No.  The article is on lithium batteries and not nickle-cadmium.  It even says so in the post.

tess said:

allow your lithium based battery

I am not a chemical engineer like some of you seem to think you are, so I can not explain any detail about how garmin charges their devices. But I can say that they DO have actual engineers that figure all this stuff out.

The watch alerts you when the battery gets low, and the users guide says to fully charge the watch. I could not find anything in the users guide that says to charge it at 40 percent and only charge it to 80 percent.

some of you are way overcomplicating this and making people think that they need to follow this 40/80 rule.

I don't know about others, but I am not going to spend a thousand dollars on a device that claims to have this much battery life so I can charge it every day or two because some people think they are chemical/electrical engineers, and maybe think they know more than the engineers at garmin (who designed the device).

Follow the documentation and you will be fine.

Does this mean apple watch users should be charging their apple watches three times per day instead of once per day?...hahaha

that they need to follow this 40/80 rule.

Where did someone say that ? I said "You have a choice.

I am not a chemical engineer like some of you seem to think you are, so I can not explain any detail about how garmin charges their devices. But I can say that they DO have actual engineers that figure all this stuff out.

Garmin doesn't need engineers to figure this out. The chenical processes that happen in a Li battery are simply known. The technology didn't just exist yesterday.

I don't know about others, but I am not going to spend a thousand dollars on a device that claims to have this much battery life so I can charge it every day or two because some people think they are chemical/electrical engineers, and maybe think they know more than the engineers at garmin (who designed the device).

I don't know how many thousands of dollars a tesla costs more than a Garmin watch. But I can tell you that Tesla only charges the battery to 90% in standard mode to conserve battery life. If you want to fully charge, you have to confirm that. I can also tell you that Garmin does not ask us how full we want to charge.

If you want to save the Garmin battery, stick to the 40-80 rule.

Or  just don't do it.

No one here is telling you how to do it.

YOU HAVE THE CHOICE.

The Li batteries in the Tesla are chemically the same.

A word about the manual and the tips of a manufacturer: is it in the interest of the manufacturer if the battery lasts forever ? 

What do you mean by "you have the choice"?! I heard that in the next firmware release, Garmin will enforce that. If user is not following, watch will provide electric shock at 80% then with every percent another one, stronger...

Oh, nice that this is finally being introduced. This has been an old suggestion for improvement.