Battery and Charging 128 GB iPhone 6s Plus

Hi Everyone,

This past Sunday (31 January 2016) I purchased the new 128 GB iPhone 6s Plus. Everything functions perfectly except, possibly, the battery. First, when I plug my new iPhone into my computer, the battery percentage goes down even though the charging symbol appears on the iPhone. Second, the battery on my iPhone seems to run down fast (but I'll admit that it might just be my perception). Third, if my iPhone is "off" (not completely powered down), I think that the battery is still running down a significant amount compared to all of my previous iPhones. The fourth problem is even more confusing for me. When I am charging my iPhone, I sometimes use a USB extension cord where one end plugs into the charger and the other end plugs into the original cord that came with the phone, allowing me to plug my iPhone into an outlet to charge while being able to be a few more feet away from the outlet. Whenever I did this with my iPhone 5c and my iPod Touch 5th Generation, things worked perfectly but, with my new iPhone, it takes an extremely long time to charge (in fact, it seems sometimes that it's neither charging nor losing charge at all). If I plug my new iPhone into a "Just In" portable charger, not only does the iPhone not charge but the charge goes down even though the charging symbol is shown--again, my iPod Touch 5th Generation and iPhone 5c charged fine with this portable charger. The new iPhone charges well with the original charger and wall adapter that came with it and charges in my car, albeit slowly, absolutely fine.

I am not sure what's going on with my iPhone 6s Plus or if all of this is normal. I know it takes a long time for my iPad to charge and I wondered if the size of the iPhone just naturally makes it unable to charge in these situations or if there is something wrong with my battery? I have Apple Care and insurance through At&t; Should I take the phone to them and have them look at it or is this just the way the new iPhone is? Would a Mophie Juice Pack help? I know it varies by what you're doing but, generally speaking, how long is the battery for the iPhone 6s Plus supposed to last?

Thank You,

Savvy Lennon