It sounds like part of your problem is you're micromanaging your phone and you really don't need to. Android can manage itself, you don't need to create your own problems. Go into you Settings >> Application manager and for each of those 'smart' booster and battery saver apps, tap the 'Force stop' button, then the 'Clear data' button, and then the 'Uninstall' button. This will not just uninstall those apps but wipe away the cruft they might leave behind.
As for apps you might disable that may or may not cause instability, just keep track of what you disable and if there is a problem, just re-enable them. Some apps might need you to reboot your phone. But for the most part you can't disable really vital things as you don't have the system level privileges to do so (that's one of the aspects to rooting your phone).
Since you recently upgraded to Marshmallow, you might want to wipe the System Cache partition. It's usually a good idea to do this after a version upgrade. The system cache partition is completely separate from the general user partition, where your data and settings are stored, so this won't affect your data. Follow the directions below:
http://cellphoneforums.net/samsung-...ring-cache-partition-rebooting-safe-mode.html
Your S5 is a couple of years old now, the battery should still be in decent condition but if you've drained/recharged it on even a near daily basis all along it might be a matter were it's just worn down. The lithium-ion batteries in our smartphones have a set number of recharge cycles and at some point they just get used up. Anyway, try cleaning off those booster apps, wipe your system cache partition, and check if you've got any apps you don't really need that are just wasting your phone's system resources. If after a couple of days your battery is still a problem, for under $10 you can buy a new OEM battery from Amazon. With your S5, all you need to do is run a fingernail along the back cover seam to pop off the plastic back cover, remove the old battery, put in the new battery, and snap the back cover back into place. Not tools necessary.
https://www.amazon.com/Samsung-Repl...=1465773298&sr=1-5&keywords=galaxy+s5+battery