There are cars that I've had in the past that don't, but I think the majority of newer ones do.

Strange really..

 

Guess it's a safety feature so people can see you braking even if you lose power/electrics etc.

 

I don't think they work without electricity though?

 

The electrical/ignition systems may fail but if you've still got a connection to the battery (assuming the battery has some charge) then they'll light up. Of course this won't be the case if the line from the brake lights get disconnected from the main circuits but I doubt this would ever happen.

Think about being on the motorway and the engine cuts out for whatever reason. You need to brake and pull over so you'll want the people behind you to know that you're braking.