There is a hidden service menu that contains a 24hr battery test but I'd leave that as a last measure. You can find tutorials online about it.
You can do a 100% charge and see what the EPA range display indicates and compare that to cars of a similar spec and date. That EPA indicated range, the normal one displayed onscreen is better switched to display % but you may already be doing that. My SR+ for example was delivered with an indicated 232 miles and the last time I checked after 3 years it had dropped to 229. Tesla always used the ~250 WLTP range online.
You could also install an OBD2 mini-wiring loom and use a reader + software for more detailed info. I've had Scan My Tesla since new but I'm thinking of buying S3EXY Buttons/Dashboard for something to play with. Quite expensive though for simply monitoring battery health.
There also ways of monitoring battery stats via the API but I've never done that.
Have a look at this link
Tesla battery degradation and health, and how to calculate
tesla-info.com