Is there an existing project or integration for #ESPHome to passively measure a 9V battery's charge?
Family member asked if there's a way to integrate a battery charge meter for e.g. fire alarms into #HomeAssistant (which obviously would mean sticking two cables into its back to directly measure the 9V block, but even more obviously can't be anything active that sits inbetween battery and alarm). I can only find ideas, not some kind of finished and proven project.
#diy