If you want active electronics you'll have to buy a preamp too.
I answered your question about what else you'd have to buy in the other thread you started -
Bartolini Pickup
But, if you keep it passive you'll only need volume/blend/tone knobs (whatever your config is). No need for a battery.
If you buy a preamp, they usually come with any 'special' pots they need i.e. potentiometers of odd impedance. Bartolini sell their preamps wired up as 'harnesses' with many different options for use on basses with different number of holes etc - look on this page and see the options -
http://www.bartolini.net/information.../harnesses.htm
There are also people like Brian at bestbassgear.com who'll wire up a preamp like the Aguilar OBP-3 for you in whatever config you want. If you've never done anything like this before, I'd recommend going this route first time - it's not difficult to apply too much heat with the soldering iron and fry a pot or preamp.