2007 Safest Vehicles Cars

What would be the effect of multiple car batteries? How to do it?
2007 Saturn Ion2 sedan is the car.
I want to run the radio with the engine off for extended periods.
Is it safe to do or could it harm the vehicle?
Like would you get more cranking amps or longer battery life or just take longer to run dead?
Does it have to be the same type or power batteries?
How would I go about wiring them together?
would it void my warranty?
Reference websites would be appretiated also. Thank you
You can put as many batteries in a car as you want,bare in mind that it adds weight to the car,gas mileage will suffer,if you want to add another battery it should be as close as possible to the original,use 4gauge cable and connect in parallel,that is NEG TO NEG POS TO POS.Some of the answers that you recieved are not exactly true,two 12 volt batteries do not make 24 only if you connect them in series,the altenator will charge both batteries providing the cables are of the same thickness and are not to long
2007 Safest Vehicles Cars

Roadfly.com – 2007 Volvo S80 Car Review
FHP to focus on county’s problems with bikes and pedestrians
MANATEE — Manatee County is far from the safest place in the world to ride a bicycle or walk on a street.