Thanks for the formatting, it's appreciated!

The MAX7456 chip on the OSD that actually does the video overlay pulls 145mA according to the manufacturer's data sheet (https://datasheets.maximintegrated.com/e...AX7456.pdf) and the Atmel AtMEGA328P MCU that runs the OSD pulls 0.2mA (http://www.atmel.com/Images/Atmel-42735-...asheet.pdf), so I really can't see why the OSD would want any more than 150mA at any time.

Most CCD cameras pull less than 50mA and a CMOS camera might pull 130mA due to the extra CPU power that's needed to handle a CMOS sensor.

This may place demands of up to 280mA on the VTX's 5V regulator, depending on the camera, so it's wise to check what your camera will draw and what the VTX can supply.

I think you'll be OK with similar batteries, but I've not tried this myself, or thought through the implications properly. You will certainly need a shared ground though as otherwise there's no reference for the UART signals.