Pipe near Aux Battery

If your hybrid battery ever gets warning lights, or gets too hot or fails in more violent ways the fan above that pipe will turn on and blow cool air through the pack that then exits out of the vehicle through this pipe via a vent on the side of the car at the end of the tube.

In terms of maintenance you need to make sure that your cooling fan is clean and not clogged with lint and pet fur.

 

that's the hose for the 12v battery vent. Previous owner might have replaced the 12v AGM battery with one that doesn't have a vent hole or probably didn't bother to reconnect it.

 

I agree with post #3. That little disconnected tube is the vent for potentially toxic 12V battery fumes, to carry them out of the passenger cabin. A proper 12V replacement battery has a vent connection for it. Batteries mounted in the engine compartment, outside the passenger compartment, don't need such a vent tube.

The "pipe" mentioned in post #2 is the much larger plastic duct behind it, from the hybrid battery compartment, which appears intact in your photo. It doesn't vent the same type of fumes that the 12V battery can.