on the 840 I swipe up (?) and swipe left/right until I find the light control panel, then override and turn off the light but leave the radar on.
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If you have good ears, it‘s possible to hear the radar working. When you hold the varia to the ear there is a hushed whirring sound while on.
(It‘s the sound a lot of coils make.)
I have a sneaking suspicion that it might be part on my HH head unit, it gets updated frequently by HH, and I think (YMMV) that at times it resets my lights preferences back to their base setting. I will find my Bontrager ION front light and my Varia light set on solid max (light setting 1 on HH) which burns through their batteries.
You’re right, it’s smart mode (listen but don’t transmit on ANT+). I added a note to my original post. So the fact that the battery is slowly draining would be even harder to detect. That’s another reason I don’t like this UX choice.
I have an OG Wahoo Element and it doesn’t support light networks so it can’t turn off the Varia when I turn off the computer. The v2 Wahoos just added smart light control and they specifically say it will control the Varia.
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First hit on a “how to extend lithium ion battery life” search:
Source: Tips for extending the lifetime of lithium-ion batteries | University of Michigan News
One excerpt:
Minimize the amount of time the battery spends at either 100% or 0% charge. Both extremely high and low “states of charge” stress batteries. Consider using a partial charge that restores the battery to 80% SoC, instead of 100%. If that’s not possible, then unplug the device as soon as it reaches 100%.
Samsung and LG suggest that their phones should be recharged when they reach a 20% state of charge. Nokia and Sony mention potential damage to their phones if the device is left charging after reaching 100%.
The rule of thumb is “keep electrons moving” which means avoiding keeping the battery at 100% or 0%.
Don’t leave the Varia sitting on the charger! Its fine to leave it in standby!
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Standby mode is likely better than charging to 100% and turning it off.
Let the blue light blink twice every 5 seconds! #StandbyMode
I’ll give that a go. Thanks
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Thanks for the advice, especially as it’s free of … charge
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I know mine is not off when I see the blue light flashing in my living room 
Thanks for the explanation of why that happens.
Yep I had this thought when others were posting about poor Varia battery life too. Thankfully I was aware of it after getting caught out when I first bought mine a few years ago, so I’m always careful to switch it off properly.
However something else for people to be aware of - Wahoo recently updated the Elemnt units to have ANT+ light control and now the red light on the Varia automatically turns off at the end of my ride, but of course remains in this standby mode. So I have to be even more careful to remember to turn it off fully and check for the blue light, without getting lulled in by the fact that the red light has stopped. Previously I would always remember.
Just say no… keep electrons moving. 5 month standby rating. Y’all need to take a class on maintaining lithium-ion batteries.
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That’s not quite right, at least not universally.
Let’s say I start with a full charge, then go for a ride and drain half the battery. Should I leave the Varia in standby mode or turn it off? Well, from a battery health perspective, I probably should turn it off if I won’t be using it for a week.
Why? Batteries age due to many factors but two of them are total number of charge cycles and what state of charge the battery is stored at. Generally charge cycles (even partial ones) matter more than what SOC a li-ion battery is stored at, so long as you don’t store it near zero charge.
So by habitually leaving it in standby mode you are putting it through more charge cycles. And if you end up not using it for a while (riding mostly indoors or MTB) you are more likely to get the battery all the way to zero charge accidentally and let it stay there because you don’t know it’s drained.
Now this is all splitting hairs, especially since we don’t know the exact chemistry and construction details of the battery nor its exact sensitivities to these factors. As someone with both academic and professional experience in this area, I can say that these can vary a lot and even the manufacturer might not have the data to prove which is better. Unless you’re using the battery in an EV it’s not worth sweating what SOC you store li-ion batteries at, as long as it’s not near zero.
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Or 100% on the charger for days
True, when I had a problem a few years back it died within a day, so it seems like I was probably not in standby mode but “light off radar on mode”. It’s easy to confuse the two, so I got into the habit of always ensuring its fully off.
With the 5 month standby rating and the Bolt now automatically putting it into standby, I should try it out again and see how it goes. The blue light might annoy me though 
Thanks for this post OP, it is useful to know. By sheer luck I think after one or two uses I happened to notice the blue light flashing after I thought it was “off” and so gave it a long hard press until it stopped and have kept doing so after each ride.
I hadn’t realised it was a separate mode and just vaguely thought it was really weird that Garmin made you press the button for ages.
I don’t think it entirely helps that on mine at least, there is no solid click to the button and so if you’re wearing gloves its hard to tell if its properly pushed down or not.
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