So when I got my S6 at BestBuy, on the day it released, the Verizon/Samsung expert was understandably swamped. I didn't want to wait and I thought I could "do it myself" so the salesman set me up and let me go home to poke around and try to figure it out alone. When I finally called BestBuy they put me through to the "expert" and he gave me a lot of info that I had been unable to find on my own. Eating Humble Pie now.
First, the phone was using Global Network mode instead of LTE/CDMA. This makes it thrash looking for multiple types of signals to connect with and you don't need Global inside the USA. Changing this was a HUGE help and I checked my husband's fairly new S5 and he had that setting wrong too.
Next, when pulling down the top status bar you get the circles across the top for Wi-Fi, GPS (location, I hate that they dumbed down this name), Sound, etc. Well, in the past you could hit a grid icon to get more of these settings. On the S6 it is a pencil icon... which to me means "edit something" not see more of the menu, so I had never looked there. Under the pencil icon I had "mobile data" off! Sheesh! To get my 4G to work I, of course, needed to turn on mobile data, which I had looked for before, but couldn't find. I also turned on power saving mode, turned off sync, though I have since turned that back on, despite causing a slight drain, I do like to sync automatically. I leave on sound, and screen rotation, and if I am trying to conserve battery, I only use Wi-Fi, GPS, and Blue Tooth etc. when needed, which I had already been doing.
He gave me a lot of charging tips, which I should have remembered from other batteries. Since we can't buy a new battery for the S6 we really need to baby the one we have. The Verizon/Samsung expert wanted me to completely discharge the battery, until the phone was "Dead, Jim, DEAD" (sorry, couldn't resist slipping in a Star Trek reference) for the first 4 charges and then charge only until it is 100% - usually less than 2 hours. I had had the phone a week by then but I did this like it was brand new. This puts a kink in my old charging habits of putting it to charge for the whole night. I am having to change my ways. I am also finding that my cheap, charging cables and plugs slow charge really slow. I think I'm going to have to give in and buy the more expensive Samsung chargers expressly for the S6 so I have one at work and a second one for home. I even bought a "Smart" USB charger with 4 slots, that is supposed to sense the right charging speed and work with Samsung products... No. Doesn't really work with my Samsung Tab or the other Samsung phones in the family. It charges, but not as fast and the Samsung chargers and REALLY charges slow with the S6.
The "expert" also recommended turning on the ultra-power saving mode while charging. I didn't know about this mode. It shuts off everything expect phone, text and emergency alerts. The screen even goes black and white. I'm excited about this mode as I often go camping for 2-3 days were I have cell reception but no place to charge and I'd like to have the phone on for emergencies. I think this u. power saver mode may get me through a week-end without dying. I can't wait to check.
I'd love to see all these tips and tricks posted somewhere as I was unable to find good documentation despite looking and I'm afraid I may have forgotten some. I am sure as time goes on, there will be a lot written about this.