ipad doesn't have enough power to run usb for any heavy devices. so besides a camera kit adapter from ipad to usb you usually need also powered usb hub.

This adapter doesn't need an extra hub, just needs to be smart enough to understand what's happening with it. When not in use (like file transfer) it changes to filling up its own battery. And voilla! (where DID I put my viola...)
-- pashute, Jan 07 2014

CyberPower Mobile Battery Powered 4-Port USB Hub http://www.amazon.c...ALQ/ref=pd_sxp_f_pt
Is this what you're looking for? [scad mientist, Feb 18 2014]

What the heck are you trying to connect to your iPad, a USB powered lawn mower?!
-- ytk, Jan 07 2014


a hard disk, or a disk on key.
-- pashute, Feb 18 2014


See link. This was the first hit on Google for "battery power usb hub". Based on reading the reviews, it sounds like there is a switch on the device. In one mode it sounds like it works as you describe, charging the internal batteries from the USB host, and presumably using power from the batteries if there is too much current being drawn by USB devivces. In the other mode it draws no power from the host and drains its own batteries (a feature not included in your idea).

From your description, I assume you may have had a smaller battery pack in mind, but 4 AAAs really isn't that big.
-- scad mientist, Feb 18 2014


I want a USB powered lawn mower, it would be ideal for mowing the green baize on my desk.
-- pocmloc, Feb 19 2014


so, it takes a scad mientist to prove that the idea was a good one, but, as usual already baked, which is also good, because halfbakers tend to halfbake only.
-- pashute, Feb 26 2014



random, halfbakery