Battery replacement truck C320?
 

I have a 2003 C320 and I just started getting a warning light saying battery low.

It started after the weather turned cold this week. The battery is in the trunk, but when I look online at the battery choices they all say, Must be vented to the outside!

The one in the trunk is a MB factory battery but it doesn't look vented to the outside. This is the first car with a battery in the truck for me. I did have a VW once and the bettery was under the rear seat.

Any suggestions on the replacement and the venting.

There should be a hole under the battery compartment that should have a grommet to let a hose pass through.

trunk mounted battery
 

hello rod

Your battery is vented with a small plastic elbow, mounted on one side of the battery. on this elbow you will find a small diameter plastic tube attached. this tube leads down to the floor of the trunk and on outside. this setup allows any gases or liquids that may seep from the battery to exit the enclosed space, preventing any potential for an explosion. it is important to buy a battery with this vent. the only exception is if you purchase an AGM type sealed battery, not to be confused with a "maintenance free" battery. I believe Interstate makes a battery for this application, check with an Interstate dealer.
Good Luck

interstate, bosch etc all have such a model. Interstate has served me excellent in my nissan.

my benz has a white MB battery - a bit old but still has the juice to fire the diesel every day. i'll swap it out with an interstate when it decides to go out

Before you replace the battery test it. The warning message you're seeing is almost certainly due to a charging system problem. :)