can i return my defective car???

so me and my boyfriend just bought an used '06 jeep cherrokee from a certified jeep/Chrysler/dodge dealership. while we were waiting for the paperwork & whatnot we were checking out our new purchase and realized the interior lights were flashing on & off while we were in the car & the engine was on (when they should have been off).
we explained & then showed this to the dealer and the head mechanic, who checked it out in front of us, saw the problem, admitted there was something not right then took the car to the garage to get "checked out". they said it was the battery and gave us a brand new battery! we have now had the car in our possession since Wednesday night. it is now friday afternoon and the same problem has come back!
what can we do about this??!!! they said we can't return it. what are our rights???

Not for one or two issues but if it is malfunctioning after that and they cannot fix it, you can take it back and demand a refund.

I cannot find a law anywhere to support returning a used car. I too bought a 06 Wrangler that leaks from the hardtop into the passenger floorboard. While trying to drain the leak we found that the plug, while intact had been cut to allow water to exit the vehicle. I am completely sure that they knew about the leak because they did not even entertain the idea of fixing it, just an immediate "we can't help you".
I would rather they fix it as it otherwise is in good repair, but I am very upset at the deception.