As to gmail, it works here. I've using the settings given by gmail support at https://support.google.com/mail/answer/4570255?hl=en
As to battery drain, I find that apps tend to eat battery time. I have a few android phones and given the proliferation of ad supported apps that drain the batter due to fetching apps, I no longer install those.
As to contacts, I think it's best to backup and restore such with an app. There are so many that I can't pick one for you.
I have a Galaxy S5 Active on ATT. It says that it's running Android version 5, but don't see anything about Lollipop, Jellybean or anything else? When I go to "About Device" & check if there are any software updates that need to be downloaded, it says yes, I then hit continue, it starts downloading, says don't leave the wi-fi area, etc., (which I don't) but it ALWAYS FAILS! Even if it says that it has completed the download, when I go to install it & reboot, it fails. Then, when I go back to check to see if the phone needs updating, it says that it is up to date & I need to check back in 24 hours?
I have been having multiple problems, but unfortunately, they are inconsistent & hard to pin down what might have precipitated it? The battery seems to drain quickly, but sometimes worse than others. I was having some problems with my Yahoo mail not refreshing for HOURS, even after I synced it manually multiple times. Now, Yahoo seems like it is better, but now I CAN NOT SEND e-mails from my G-Mail account! They keep failing & the error message that I get is that I can't sign in to the account? I also get a message that it can't authenticate the server. What does that mean?
I rebooted several times, even took the back off, removed the battery & re-inserted it. After a couple of days when I reopened the e-mail from the Outbox folder & tried sending it, it worked! This was not after I had done anything specific. I assumed that either Samsung, AT&T, Google or another conflicting App had figured out that they had a bug & fixed it, but then a couple of days passed & I'm having the same problem AGAIN.
I started having problems with the G-mail after I had downloaded a couple of Apps. I downloaded them from the official Google Play & they seem innocuous, like the Safeway App, the Whole Foods App. It's scary to see what "permissions" these Apps have & *** do they even need them for? I don't know if any could have changed my settings & I don't know which settings I should look for to tell if they might be suspicious? I'm also running Clean Master & Avast Mobile Security, but I have had them for a long time. They shouldn't be a problem unless one of their recent updates changed something or it conflicts with something else?
I recently downloaded Google Drive for my phone. You would think that Google's own App would play nicely with G-mail, but it might have changed the Sync settings? Unfortunately, I don't know what the setting were BEFORE or even what they SHOULD have been? Is there anyplace on-line where I could find the standard settings? I wish that there was a way to SAVE the settings before you install new software & then be able to ROLL BACK to them after you discover a conflict. One good thing from the old Windows days, you could refresh to the last stable state. Maybe that's too much to ask. Sigh.
I'm posting this here & hopefully another couple of places. (any suggestions?) I have searched on-line & have not found my exact same problems described, either the issue, the carrier, the phone and/or the software is different. One forum suggested to change the port on which the outgoing server uses. Before I do that, I want to do some screen saves of what my original settings are so that I can change back if I need to. I don't know if those setting are correct, but want to be methodical & see which change might make the difference. Is there some other way to save the setting to a file?
Does anyone know if there is a place on the phone where you can view the "History" of the changes, both when Apps were downloaded & updated? I looked at some of my new Apps & it doesn't say the date that they were downloaded, which might be helpful in figuring out if any of them coincide with any problems. I don't want to just uninstall them yet until I figure out which one may have the bug, or which one might have altered some settings.
I please don't just tell me to do a factory reset, like it's EASY. I have had this phone for over a year & I have done so many different customizations, setting ringtones, setting up notifications, etc., etc., etc., I don't want to have to start from scratch again. & another thing; I had contacts from the Sim card on my old phone, my Facebook contacts, some from my G-mail account ( which for some reason had stopped syncing?) and when the guy @ Best Buy transferred settings from my old phone to the new. I ended up with multiple copies of some contacts so I had painstakingly merged them, which took a lot of time. Then, after one of the times that AT&T updated the software, all of my work was undone & was back to having multiple entries for the majority of my contacts. Then, just recently, some of the contacts that I use the most just disappeared & I had to recreate them?
If I didn't need this phone for so much I would just throw it against the wall.

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