PSA: Why Your Varia Battery Randomly Dies

I think I know why there’s mixed reports of Varia battery life in the Trek CarBack thread. I thought my battery on my RTL510 was getting pretty bad but it is a combination of bad UI and human error.

The mode that I use most often is daytime flash mode (light blinking completely off to bright on). When I go to turn it off, I press and hold the button for a few seconds and it stops flashing. However, if I happened to hold that button just slightly not long enough, I haven’t turned the Varia off, I’ve just moved it to the next mode, which is light off but radar still on (edit: it’s actually “smart mode”, where it listens on ANT+ but doesn’t transmit). The only way to tell is to look at the small blue light on the side, which only flashes once per 5 seconds. So it’s easy to drain the battery by accident.

Now here’s the real kicker. If you stick it on the charger when the radar is still on (since you think it’s off), it won’t turn off (presumably so you can run an external battery pack on the road). So it won’t even charge properly when it’s put on the charger (maybe it will with a high enough current charger, IDK). So you go to ride and now the carry life is really short.

And once the battery dies, the unit goes back to default mode (light on) upon recharge. So you never realize your mistake! Then the cycle repeats intermittently depending on what mode you were in when trying to turn it off and if you held that button long enough.

Now I always try to remember to check the little blue light after every use AND before every charge. I really wish Garmin would make it so holding the mode/power button did nothing if you hold the button for more than 1 sec but less than 5 seconds or however long you have to hold it to turn the Varia off. That would greatly reduce the risk of accidentally turning off just the light and not the whole unit.

Edit: When the main red light is off but the blue side light is double flashing every 5 seconds, it means that the Varia is in smart mode. That means that the radar is off and the Varia is not transmitting but it is listening for an ANT+ signal from bike computer to turn on the light and radar. This will use a certain amount of battery each day that it is in this mode. If you do hold down the power button for a full two seconds (feels more like three) the side light will turn completely off, indicating the Varia is fully off. There should be no appreciable battery drain then.

If you have a Garmin Edge XX30 or later or a Wahoo Roam v2 or Bolt v2, then it supports the smart light control and you can just control the Varia power from there if you don’t mind that very slow battery drain.


When I hold my power button down to turn it off, after about 2 seconds the blue light comes on, then about another second later it turns off. That’s how I know it’s properly off (my Garmin also then immediately chimes to say the light network connection has been lost). Works for me.


I have definitely done this before and thought my battery was dying. It is very annoying. My Varia also has severely diminished battery life in the cold. Every winter I think the thing is on its last leg and then the weather warms up and I get much better battery life.

I get it. That is a known issue with batteries. But it seems the Varia is more effected by cold than any of my other lights/computers/axs batteries/etc.

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Thank you @huges84 for posting this. I didn’t even know there was a setting for radar only, no light. The Varia ought to be programmed that it turns itself off from radar-only mode after so many minutes of not being connected to a head unit. That it apparently doesn’t is a great surprise. Like I said, I didn’t even know there was a “radar only” mode.

I hate to say this explains so much - I like the others am thinking my 515 is on it last legs and then the next ride the battery performs like a champ.

So if I read this right, the tiny blue flashing light every 5 seconds is saying its not off but radar only? I see the blue flashing light all the time while my bike is in the rack or on the charger, I thought it was peculiar, but it just did that.

Small life improvement - Thank you!


Literally just yesterday I put a strip of electrical tape over the flashing blue lights on both my Varia units. I was sleeping down in the basement for total darkness as I needed to catch up on sleep. I couldn’t stand both Varias flashing blue. I had no idea they were actually on :rofl:

As my grandfather would have said (in less colorful language), it’s funny how often RTFM is the answer.


I’ll have to look at mine, but I never use the blue button. I always allow my head unit to control the Varia, and always have a blue flashing light. Battery will last on standby for days fine.

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I dunno, my radar is off and the blue light is flashing.

My Garmin 840/530/520 bike computer turns off the Varia when I power down the 840/530/520.

When off, my RTL515 has a flashing blue LED:

While on vacation I’ve left my Varia like that for a week or two, and come home and it is still charged.


Same here. I never touch the power button on my varia so the blue light blinks every 5s or so but I still get solid battery life years later after basically daily use.


@huges84 you can check the “solved” button! Great post!

I honestly was wondering what the problem was in that other topic. My Varia is like 5 years old and I’ve never ever had a low battery issue. I don’t do 5 hour rides with any regularity but I’ve often done several rides without charging the Varia between rides. I think I’ve experienced a low battery once or twice?

So if I read this right, the tiny blue flashing light every 5 seconds is saying its not off but radar only?

I am not sure that’s true. My impression was that the unit was in standby mode and that it would receive ANT+ signals but not transmit. When you switch to standby mode, my Wahoo head units lose contact with the Radar and give me a pop up message to that effect. I am not sure how long the device is supposed to last in standby mode. On this thread, two people say that they remember figures like 30-60 days. I can’t find actual figures.


Yes. FWIW I’m in the garage looking at a Varia 515 in standby mode. Blinks blue twice, then repeats after 5 seconds.

Good to know in case my blue light comes on.

This is the easiest way to ensure it’s completely off. Just turn off the Varia before the Garmin. The head unit will beep and tell you the connection was lost. Yes, the blue light will flash every 5 seconds.

On a side note, I’ve done similar with my head unit, where I charged it and threw it in its storage space thinking I had turned it off, but it was in standby mode, so the battery had drained the next time I went to use it. I now ensure it’s fully powered down before putting it away.

Okay - so blue light flashing in standby mode is normal. Back to the regular charging, taking it off the plug just prior to long rides.

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On a kind of related issue.

When i stop for coffee, i like to turn my 515 off so others are not disturbed by radar notifications and flashing lights.

I turn the 515 off completely, but is there a way to achieve the same effect via the Garmin headunit that will reactivate it again when i start riding again?

For me locking the garmin after pausing the ride turns off connected lights. So hit the stop button and then sleep the head unit and the sensors will turn off, when you start again wake up the unit and it will turn the sensors back on.

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Rode 6 days ago, last time I used the Varia radar. Its been in standby with the 5-sec blue blinking light. Radar is showing fully charged. A little over 2 years old. :man_shrugging:

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I was talking about my head unit