Confirmed RCT715 works with backup battery

Thanks for the info

I bet you’ll see third party options for alternative mounting options before long.

The seatpost mount suits me but I don’t have a regular seat bag. I use a Silca seat roll fastened to the top of my seat stay triangle.

Awesome.  Thanks for sharing! 

I wonder if when the battery is at 100% and you plug in an external battery....   Do you think it takes power externally and bypasses the internal battery all-together to run the device?  Or rather, it keeps using the internal battery while charging it?  

The reason I ask is, if it doesn't wear down the internal battery and bypasses it, I could double it up as a dash cam in my car.   I wouldn't want to do this on a regular basis if it wears down the internal battery.  I'd imagine nobody could really answer this except for Garmin directly.

Do you think it takes power externally and bypasses the internal battery all-together to run the device? 

I'm not well-informed enough to have a definitive answer for this but I have my suspicions:

This would be specified by the USB-C standards, not Garmin. If I were a betting man, I'd think USB-C is smart enough to shunt power from the external power source directly to whatever needs current and bypass the battery.

The possible issue with that bet is that li-ion batteries don't last long when they're always fully charged. If you bypass the battery completely, whenever it's at a full charge, a backup battery is going to cut into the lifespan of the internal battery.

You would get around that if you let it float within a range. But is that really part of the USB-C standard, or a built-in power management chip like you have in a cell phone?

I'd say it was much more likely that the light would always run off the battery, and never directly from an external power source as it keeps the design much simpler and avoids unnecessary additional costs for something that would not be of any significant benefit. This tends to be a standard design, which is why most portable electronic devices won't run off the mains if the battery is missing or unable to hold a charge. You can normally test this on any device by letting the battery run totally flat (so the device won't even power on), then plug it in and try. Usually, the device still won't power-on until the battery has received some charge.

Were you able to get accurate speed overlay?

The speed overlay on mine is only accurate in the first 5minutes of the ride...

Thank you!  Was going to test this. This is an awesome change and was an issue with the older units for really long days. I have a small sharper that will be perfect. 

Did you find a smart way to fix the Varia on the frame instead of seat tube?

I don't know how to fix it while doing backpacking!