Sorry about the rough times after updating jayshaa. I have some suggestions that can help. You can use the tips in the link below to help get the most out of each charge.
Keep in mind some apps may not be as "battery friendly" after a software update. This can cause you to see a difference in the battery life. It could take an update on your 3rd party apps to help them use the battery life better with the new software.
You could try a simple restart to see if that helps the sensors respond properly. The last step would be a master reset. I suggest keeping all 3rd party apps off the phone until you notice it's working.
Well -- I also face the same problem, wherein after the marshmallow upgrade, the battery on my S6 is draining very fast and unless connected to charger in Ultra Power Saving OR in switched off mode, the charge doesn't even increase.
As per the battery usage screen, the top users (80% of battery) are always the below:
Screen (already setup as AUTO), Cell Standby, Android OS, Device idle and Android System
This is not being caused by any 3rd party app but should be due to the upgrade.. Will appreciate due review and suggest / provide a resolution.
Hmm, you too huh? Bummer. shsr have you tried the battery saving tips in the link I posted above? Since your screen is the top battery user, have have you tried dimming it or changing the timeout setting? If things like this happen after an update, it's highly recommended that you test your phone without anything 3rd party installed. Even if it's for just a short while. It's worth a shot since it can help with the battery life.