The amount of onboard telemetry you can get at varies between receiver brands. The one you’ll be most sensitive to will be Receiver battery level which is really jolly useful to know.
Spektrum have a simple approach which is to automatically pick up the receiver voltage and display it for you.
It’s not on the Home Screen unfortunately, but if you roll the scroller bar without pressing it down to click, you go through just a few menus. The last but one in the sequence is labelled “Flight log” and you will see Receiver voltage very clearly on there whenever the boat is within telemetry range.
Datchet Radio Sailing Transmitter Manuals - Spektrum 