Monitors were still 12V inside last time I checked (5 years ago), they're basically integrating the PSU into the monitors because they use less power and can be

Monitors were still 12V inside last time I checked (5 years ago), they're basically integrating the PSU into the monitors because they use less power and can be smaller/run cooler. It's very likely you can just bypass the internal PSU on any monitor and power it straight from your battery. You'll just need to take it apart, which can be hard depending on the housing.