1) Not "until you feel a recharge is necessary", but until the phone tells you to recharge it.
2) That probably won't show anything helpful - the screen and Android System are probably using most of the battery, and that's normal. If some other app or function is using most of the battery, that would most likely be the problem.
3) The battery should be conditioned. (That should be done to every LiIon battery you don't know the condition of.) Fully charge the battery - until the phone tells you to remove the charger. Use the phone without recharging it until the phone tells you to recharge it, then fully charge it. Repeat that cycle (full charge, full discharge) 3 times.
4) The best battery life (time between new batteries, not time between charges) occurs when the battery is charged at about 40%-60% discharged. Don't blame the manufacturers, that's simply how the laws of physics and chemistry apply to Lithium Ion batteries (and they're the most power dense [most power in the least volume] batteries we currently have).
(BTW, although Ihaven't done ny tests, I don't think that "super saver mode" in the S5 is too much more than a gimmick. It turns off certain functions [which you can do by hand], but getting 2 days from a phone you're actually using, these days, is asking a bit much for the stock batteries. I can easily get 3 days, sometimes 4 days, if I keep my Note 3 on normal power saver, with the screen turned off, in Airplane mode, and don't use it or have any programs doing anything. But make phone calls, or even read web sites all day long, and you're not going to get 2 8-hour days on most phones.)
BTW, it's not "the S5" that's the problem, but it can be your S5, so that 2 week period would be the difference between having the phone replaced with a new one or a refurb. The S5 is a good phone, and not prone to abnormal battery use. (So if you exchange it for some other make or model phone, you're starting with a whole other set of quirks, and the 2 week period probably won't reset.) Between the S5 and my Note 3, I still prefer the Note 3, but I'd feel a lot safer using the phone in the rain if I had an S5.