Passthough runs on USB power, and there are cheap ones with high dollar ones. Now they key with the Passthough also is that you can use them in cars with a high powered USB charger for PSP I-Phone and what not. They also make battery packs that the passthough can also plug into.
The 510 has a rechargeable battery in the normal passthough around that is rated around 300mah. It last a long time not even hooked up to a USB port.
The 901/801 are normally straight passthoughs that have no battery, and they dish out what ever voltage the USB port is giving it.
I have 3 of them myself. I have the 510 with the battery on it, and that is great to have for weaker USB ports. It always dishes out the same voltage.
I have two straight passthoughs from
Vapor Kings - DSE801, RN4072, DSE901 and RN4075 e-Cigarette supplies that fit on the 901/801 both run on normal USB voltage at 5v. Which is what I say the perfect voltage for the 901. They are very cheap(at least to me 16 dollars or so with free shipping) they also have the standard cut off time on them, and they also have the LED on the front like the standard batteries. Along with a thicker than normal cable that is on a lot of them.
Now the top dog, and cost more is from
PureSmoker.com - Home of the USA Built PV !!! which has a very thick wire. They also have a power coated paint job on them. The adapters for the Prodigy screw right on top to let you switch atomizers.