Dynamo Lights

Daylight:

• Garmin runs on its own power
  
• Dynamo charges cache battery and, when that's full, powers/charges Garmin
  
• If at any point during the day the Garmin gets low on power then charge it from the dynamo instead of the cache battery
  
  

Night:

• Dynamo powers lights and Garmin
  
• Cache battery is a backup
  
  

The power required to keep the Garmin ticking over (not charging) is a lot less than running it and charging it.