Essentially a USB pass
through (or "PT") works the same as a regular e-cig battery (i.e., you screw in an atty or carto and
vape), except it plugs in with a USB cable to a port on your computer or with an adapter to another power source (e.g., car cigarette lighter port or wall outlet). It provides a continuing source of power to your atomizer, rather than running down your portable battery. Some of them (see further below) even deliver higher voltage than the standard e-cig battery. The price you pay is that you are tethered. [Therefore,
personally, I don't like them.]
Some fat batts can also be used as a passthrough. The Riva is not one of them. [Still a great PV though.] Ones that can include the Leo and Lea (as well as a
special version of the eGo).
Most PTs are dedicated to that purpose. Those that operate at the same 3.2V as the eGo or Riva (assuming that you don't have the Riva-510 "Special Edition", which is 3.7V) have an inline battery and can be used with some USB/car adapters, both of which are carried by many suppliers, e.g., LiteCigUSA: $10 each for
the PT (shown immediately below) and
USB to Car Adaptor (shown further below and which has even greater amps capacity than you would need for this PT).
I am most familiar with ones that operate at 5V: providing a much more intense vape, but which should not be used with LR atomizers or cartomizers (with the possible exception of the Smok Tech Dual Coil cartos that are effective at various voltages). The least expensive 5V 510 PT I know of is from
ElectronicStix: $13 ... which also carries a
5V 2 Amp USB Car Adapter (appropriate for a 5V PT) for $11.
MadVapes sells a very similar
5V 510 PT (made by Smok Tech) for $17 and a
2 amp Car to USB Adapter for $7.
So $24 to either supplier buys you a 5V PT and an adapter for using it in your car. And MadVapes also sells this
2 amp AC to USB Adapter for $7 (to use either of these 5V passthroughs at home or work).
There also are more expensive (and sturdier) 5V PTs, e.g., this mid-priced
Acrylic 5 volt 510 Passthrough for $39 from MadVapes (currently out of stock) or this top-of-the-line
5V VP-PT (510 or 801 connection and which comes with its own USB/AC adapter along with acrylic stand) for $80 from VaprLife.