How quick to charge to 80%?

I'm not sure how much watt the iPhone internal charging IC can handle, but the iPad charger definitely charges the iPhone faster than the 5w adapter. Did anyone ask Apple if this can be recommended?

 

Apple says it's ok to use the iPad charger to charge the iPhone. Yes it will charge it faster to 80%. Charging Li-ion batteries at a lower current though, using the 5W charger provided, will extend it's useful life. Rapid charging of all li-ion batteries is harder on the battery than using a lower current charger.

 

From 0% to 80% I have found that my 6s Plus will add one percent to the battery charge for every minute.

15 minutes will get you additional 15%

 

Battery size in mA times 0.80, divide that number by the charging speed in mA and you'll get hours. Times that by 60 to get minutes.

 

^^
That method (may) only work for a new fresh battery. Old batteries charge faster but hold less charge because their capacity has diminished with age. They essentially become smaller batteries.