I don't think you will be able to use a USB port to charge as USB only outputs 5V and the SP3 charger is 12V.
You cab use a battery like the Intocircuit.
I have the 26000 mAh model that I used to use to charge my SP1.
I would caution using these cables though, and say if you do use them, don't leave it unattended.
I used an aftermarket cable on the SP1 and luckily I was watching it when I saw it melt and quickly detached it.
That said, I have used other aftermarket charging cables on the SP1 with no problem.
It's just one of those things that you don't really know what the quality will be.
I want to get a cable to charge my SP3 from the Intocircuit battyer. The one in the OP will do the trick. I'm just a bit hesitant about the quality.
I'm thinking that since the battery life is a lot better than my SP1, I can handle just using the original charger in a power outlet for now. But, am interested to hear if anyone has used the cable in the OP.
Rich
[edit] image doesn't seem to be working, so here is the link
https://onedrive.live.com/?cid=20d6b2fa68a06dd7&id=20D6B2FA68A06DD7!5656&v=3&ithint=photo,jpg&authkey=!AFOTBjzdf_sI5co
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