Which Garmin do you have, and how long do you plan to be out there? Basically, you need to calculate how many mAH you need from the charger to know how to size it.

Something like the 830 has over 20hrs of life with GPS, so probably won't even need a re-up. I think its battery is 3100mAH.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

Garmin 520. I did a 220 mile gravel ride last year and it started low battery warning ~150 miles. I found a really small and lightweight charger on Amazon that advertises 3350mAH. I don't know how that matches up to the 520.

That should get you one full recharge....which is more than enough.

For $$$$, Garmin has a Cadillac option: https://buy.garmin.com/.../US/p/571552#devices
It's 3100mAH @ 5V.....so basically the same battery that is in the head unit.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

This one... https://smile.amazon.com/...ge?ie=UTF8&psc=1

Just plug it in from the start so you don't have to screw with it during the race. As a bonus, the screen backlight stays on when being powered by an external source, so you'll be able to see your screen if you're out there after dark.

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Steve

"If you ain't first, you're last." Reese Bobby Talladega Nights

I love my Anker 10,000