I recently bought a cheap/Chinese (shipped from China), cigarette-lighter socket-adapter for two USB ports.
The adapter displays vehicle electrical system voltage. I will post a report on how well it works on a 6v system.
On my small 12v truck, it displays a little less than 12v when the truck is off, and it shows around 12.4v when the truck engine is running.
I’ll test it on a 6v truck (idling, and turned off) - charging a GPS and a cell phone (separately, and together).
