abidemi said:
@Gabriel
It’s dehumidifying, but because it’s releasing the water back into the garage, it’s not making a big difference.
Exactly. If you catch the water, it’ll have a better effect as a dehumidifier.
Just condensation from the AC system.
If you don’t charge it overnight, do you still get the musty smell?
Does your car have a heat pump? It could be pulling moisture out of the air if so.
If there was actually water coming out of the battery, that would be concerning. But yeah, your car will heat and cool itself while charging, causing condensation just like any AC system.
Honestly, everyone with a garage could probably use a dehumidifier.
Cars need breaks too! Don’t you wake up at night for a bathroom break? 
Probably just condensation. The battery pack is sealed.
The battery and HV system are designed to be sealed, but if your car has a heat pump, it may also be causing condensation.
sorphia said:
The battery and HV system are designed to be sealed, but if your car has a heat pump, it may also be causing condensation.
The pack is mostly sealed, but it has pressure valves for releasing hot air during fast charging. Dirt or ice can damage these valves over time, so rinsing under your car regularly is a good idea to keep things clean.
@MAKENA
According to the service manual, if pressure inside the battery case goes too high, the case itself could deform before the valve releases any air. Just something to keep in mind.
This is pretty common. After I pull my car out, there’s often a small puddle left on the garage floor. On cold, wet nights, it can even fog up the garage windows and make it feel like a steam room. I usually crack a window for ventilation if it’s not too cold.
If you drive in rain, you’ll likely bring some moisture into the garage that can stick around. But if it’s been dry and your garage is still humid, maybe check for clogs or water getting trapped under the car.
Doesn’t sound normal to me. AC can cause condensation, but in freezing weather? It’s possible it could be snow melting from the battery heater.
You could try charging at a lower amperage. It’ll take longer, but it may generate less heat and help reduce condensation.
The AC compressor cooling the battery could create condensation, especially in humid environments.
Your battery pack heats up during charging, which then cools down and produces condensation. This plus any mildew already present in your garage can make it feel damp. A dehumidifier should help if the garage is tightly enclosed.
Your cooling system might be leaking.
diallo said:
Your cooling system might be leaking.
Unlikely, since coolant is usually colored, so you’d notice it right away.
diallo said:
Your cooling system might be leaking.
Even though this is probably just condensation, it’s still good to check for leaks since it’s a common worry.
OP didn’t actually say the fluid was clear.