Powering a large device (like a Macbook) from USB-A port

Hi,

Recently we've been asked again if you can run a Macbook Pro from a USB-A battery.  The kind that powers Phones.

Here's what we said:

You can only use batteries that have high power output, like 16-20vdc and about 4amps.

It is impossible to Power the Magsafe Macbooks from USB.  

It's like asking a motorcycle engine to pull a Semi-truck.

In technical terms, USB is only 5v, and max at 3a.  That's only about 15w.  Your Macbook starts at 60w (Macbook Pro 85w).  There is no way to up-convert 15w to 60w.  It's like asking for magic.

Stay Powered,

Mike