Are you worried about how much you should charge the Galaxy S5 initially? I have had an S3 and an S4 before and all I did for first time is charge it to 100 percent then when it got low to 20 percent I charged it up to 80%. Like a Prius car I kept charge at 80% Max which they say extends battery life. You can read my long article of the S4 regarding this first time charging matter. Best thing you can do for your S5 or any kind of device with a battery is to charge it less often. This also is true for LG G3. The less often you charge the longer it lasts, even Apple says that. Some people say you should keep it charged for 16 hours the first time but I find that wrong. I get great battery life and when I don’t do stuff that is data intensive or call people frequently, I notice that my battery life is 3 days without recharging.
Older batteries of the past required lots of charging the first time, but modern battery technology doesn’t require that.
You should only completely discharge your battery and charge to full every 45 days.http://www.techlivewire.com/1068/how-long-to-charge-the-galaxy-s4-for-the-first-time.html You can ensure your battery doesn’t die out quick by getting rid of apps that eat up battery life like Tango. Tango actually sends messages to all your contacts without your permission so make sure you keep an eye on your apps, and look at your battery stats to determine which apps are using the most battery.
You don’t wanna end up buying a new battery too soon (and believe me, batteries for high end phones like HTC One M8 or Galaxy S5 are getting expensive). Also, you should avoid charging your phone overnight. Even though modern phones come with electricity cut off after battery is full, I still would not leave it in charger past 100%.