techsupport

Wait do you want to have some sort of security camera when not using the car or more something to record when driving?

Do you want to stream the camera with the phone? If so that'll take quite a bit more power than you're expecting.

If you want to record when the car is sitting idle, I wouldn't connect it to the car directly as you'll probably drain the battery (the capacity of those isn't huge and I bet you'd drain it enough in <10h)

If you want the phone to be able to record and stream over 2G / 4G for a full week, I would do the following:

Fully charge the phone, turn off the WiFi, set the app to start the stream, and make it look outside a window. Then check in every hour to see when the battery ran out.

Once you know it take X hours to drain the battery, look up your phone battery capacity (ideally in WH to get an accurate result, but mAh is fine), and then you can do the math:

There's 24*7= 168h in a week You need capacity for 168/X hours (the time it took to drain the battery) Multiply by your capacity C

So in the end you'll need a power bank that has at least 168/X*C Wh.

If you only have the mAh rating it's a bit more math, happy to help with infos if you need it.