I was finally able to charge an iphone 11 from the Garmin Messenger reverse charging, using this Anker Poweline II cable
I haven’t found any hands on testing of this feature on-line, so thought I’d share a few results:
20 min charge #1: Garmin Battery 80%->58%, iphone11 battery 48%->55%
20 min charge #2: Garmin Battery 58%->35%, iphone11 battery 55%->63%
When used like the Zoleo (I used one last year) without navigation, the Messenger has great battery life so draining it for an iphone charge or two is no big worry. Turn it on when needing SOS, text or weather, leave it off otherwise. It uses very little battery that way.
This is a useful safety feature to re-enable GPS navigation capability in case the phone battery dies if accidentally left on with a battery hogging app (anything hunting GPS satellites for example).