andrej567 as GrapheneOS account stated further up, vast majority of users report battery performance on par or better than the stock OS. Whatever issues, I would say rely on case by case setup and need to be addressed as such.
So, if you have issues with yout bettery performance, look at your Battery use section and Running apps (which are in Developer settings) and try to eliminate the culprits.
Other reasons may be many, like the way the network is used, screen brightness, overall screen on time, but the Battery use should give you a good first indication.
If you need to say take a long walk in the forest and you experience battery drain, just put your device in airplane mode or completely turn it off. That way, should you need it, you will have it on you without having to worry about your battery. If you for some reason need to monitor the length of your walk, just get a cheap pedometer or a standalone fitness tracker/watch. Like I said many times in the past, there are privacy friendly alternatives to everything that don't have to wreck your battery or the wallet.