Transient Thermal Simulation with small slots for air flow.

Hello,

I'm trying to model a balloon launch with temperature changes with time as it rises.

The current simulation with the payload box entirely closed shows the battery getting too hot, so we definitely need a slotted hole for extra convection near the battery to better cool it down, but I don't know how to model that. I've tried adding a convection value along the sides of the slot or on top of the battery but that just gives unreal values, such as 20000°C battery. I've also tried adding an external temperature to the sides of the slots and that is better but it only works for conduction and doesn't simulate cold airflow through the slots to cool down the batteries. Any suggestions?

Thanks,

SolidworksSimulation