Hi everyone,
I have an older 300 (2006) and I recently just had to change the batthey in the trunk. I contact a business and they sold me a battery. But now that I think of it.... should it have a venting tube?

 

Charging a battery produces a small amount of hydrogen gas. Hydrogen is very light and tends to rise. The trunk is not sealed enough to confine it. What little that might accumulate is not enough to be dangerous. The usual flow for air that is blown into the car through the heater/air conditioner is out through the trunk, so it's well ventilated already. Don't lose any sleep over it.