I use the Macbook Pro 15' Retina and i would know what happen when i use the Macbook Air Charger 45W ? is it work fine ? because it's less than what my macbook pro 15' need
MacBook Pro with Retina display, OS X El Capitan (10.11.4)
You can use a charger with MORE capacity and it is no problem whatsoever (the power adapter is just physically heavier to carry around).
This question is usually asked about using the 60W unit where an 85W unit is standard. You are going down TWO steps, and will run into more issues more quickly.
Using a smaller charger may mean that you cannot charge and Run at the same time. When you try this with a much too small power adapter, it will "borrow" electricity from the battery to run the MacBook, so you may find that running with the smaller power adapter connected still results in a slight net Loss of battery charge over a period of time.
If you connect the smaller adapter with the Mac Off, it will charge, but more slowly, and you need to keep an eye on the power adapter to be sure it does not overheat.
In the long run, this is not a really good setup. But it can get you through a tight spot for a little while until you can get the right power adapter.
The macbook charger
