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You don't need to buy an iPad charger just a USB wall adapter that has more than 5 Watt output. iPads ship with a 10 or 12 watt wall charger and the same lightening cable that the iPhone ships with.
Go to settings and put the phone in battery save mode. The phone will automatically turn it off when the charge reaches the 80% range. I use it daily anytime I need a quick charge on my iPhone 6s Plus.