I don't think it can handle the power (400 mA) for a pass-through as a standalone power supply.
I built one using the same eBay board but use a 14500 in line to act as a buffer. Just unplug when I get out of the truck.
I have also used a cell phone charger (12v cig lighter type) it too has the charging circuitry built in so as not to overcharge. I think they all pretty much have the same chip as they are all rated about the same.
And it has the nice curled cord and mini USB M connector already on it.
I guess I could sacrifice one to the e-cig deities as I have several from old phones and they are only a buck or two on eBay with free shipping from China. (Don't know how they can do that)
I bought 2 lots (20 ea) of mini USB DIY connectors just last week (waiting to get them still) that I am going to put in ALL my mods from now on. $5.99 and free shipping.
20Pcs Mini USB 5Pin Female PCB Socket Connector DIY