charge via portable external USB battery, how long does it take?

[Touchpaddle]

there are are few highly rated portabel external USB batteries for sale on A _ _ _ _ n.com.

They range from 4000mAh to 7000mAh and fit in the palm of your hand. They have USB
outs that connect to the phone.

How long does it take those batteries to charge a Galaxy Nexus from dead to 100%?

Thanks!

 

[yosteve]

I have the 8300 once, I've only done it once, seems like 3-4 hours.