850 Battery Life - OUCH!

Setting screen brightness to a fixed % rather than Auto might well increase the rate of battery burn unless you're riding in bright sunlight.  If you're not riding in bright sunlight you'd be better off using Auto or a very low set %.

Do some testing:  Go to System > Display and you'll see the Auto Brightness toggle.  If Auto Brightness is toggled 'on' the field below (Brightness) is greyed out.  Now toggle Auto Brightness to 'off'.  The Brighness field below will show what the brightness of the screen actually is as %.

It's a bright day outside with high cloud but no direct sun.  When I toggle Auto Brightness to 'off' the unit tells me the screen brightness is 80%. Very readable.  If I go indoors, the screen stays at 80%.  But it I toggle Auto Brightness to 'on' the screen dims a lot.  Toggling Auto Brighness to 'off' tells me the screen is at 10% Brightness, still very readable, and that's the lowest it can be, even in a totally dark room. 

So here's the thing:  If you want to extend battery life by switching Auto Brightness off, you'll need to be very sure to adjust the % you choose depending on ambient light or you might be running a brighter screen with faster battery burn than if you left Auto Brightness on.  You might find 50% brightness is OK on sunny days (or not) but as the sun goes down you'll be losing battery life if you don't adjust it down and down.

Better for most I think is to leave Auto Brighness on and let it do its work.  Get used to charging as often as you charge other batteries and if you have a crazy long ride comeing up, bring your 840 or 830 out of retirement. Or buy a battery pack.

It would be more useful if the system used Auto Brightness all the time but users could limit the maximum brightness to whatever % worked for them.  The current choice bewteen Auto and a fixed % isn't so usefull.

On 40% the screen is slight darker than auto mode which was too bright for me…is not so much difference

Last rides was on road with all sensors ( PM, Varia, HRM, Speed ) with no map on the screen…The visibility is like 840 on auto brightness with backlight off.

I guess, that we can debate here until the end of time. However, I think there are only two options for those looking for a new device now.
 
(1) If you care about battery life with a display that was and is perfectly OK, go for the x40.

(2) If you do not care about battery life and want a super bright display, go for the x50

Those of you who bought the x50 and are now riding with 40% brightness have not made a smart choice.

That’s my opinion ‍♂️

i wonder if it needs a brightness threshold setting so you can set a baseline for how bright you want it to be, relative to the ambient light. it seems every firmware update includes "Improved auto backlight performance" so they're trying to tweak it but comments like "auto mode which was too bright for me" suggest some people don't need or want such a bright screen and would do better with saving battery life. the only option currently is to apply a fixed brightness which as has been said, means you hardly ever have the most appropriate brightness/battery trade-off