Can I plug the v3 into my cigarette lighter using a usb charging device ?
Should be able to. I do so with a V2 in the pickup - and have for well over a year.
V3 has the same power requirements as aV2.
5 volts/1 amp. You will need to be sure the charger you use converts your vehicles voltage (usually 12v) and provides at least 1 amp and has the correct connector.
Does it drain your vehicle battery ?
I live in my van, and want to use it for security, do I have to be by wi fi or just on my phone ?
Would it use alot of data on my phone ?
Eventually it would drain the battery, but at a quarter amp, it would take quite a while.
As for WiFi, it depends a little on what you are trying to do. In order for the camera to send alerts, it MUST have internet connectivity. That connectivity can come from your phone acting as a WiFi hotspot, some other device acting as a hotspot, or some other source of WiFi (such as a public WiFi provided by a store or restaurant, etc.
How much data it uses would depend a lot of what you are doing with it. If you are connected and watching most of the time, that would use a lot.