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Battery cooling?

4K views 18 replies 10 participants last post by  LittleRedRidingHood 
#1 ·
I have had my S40 T5 AWD for about a year and a half now, and I just this week figured out what that duct in the hood was supposed to be for. My investigation was probably hindered by the fact that I'm missing the top of my battery box.





Questions:

1. Is battery overheating really such a risk that it needs its own cooling duct?

2. Am I experiencing some kind of risk by not having the top to the box that meets up with the duct? And if so, where can I get one?

Thanks!

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#2 ·
I don't think the duct is for "cooling" purposes. since most cars have the battery near the engine. To me its for venting the gasses that come out of the battery.
The battery won't go anywhere since you have the holding bracket. The only risk I think is having the terminals uncovered. I didn't had a battery cover for more than 2 years on my car until I found one in the junkyard for dirt cheap.

The of the cover is P/N: is 31301483 and costs ~$30 brand new online
 
#4 ·
Thanks for the part number. FCP Euro didn't have fitment, so it didn't come up in my searching.

I do think it is designed to cool though. Were it simply to vent, it seems it would have been much easer to vent to the rear instead of constructing a series of ducting all the way to the grill (which seems like it would move air from front to rear rather than vice versus).

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#3 ·
From memory, the Focus ST Mk.II (the engine bay of which is identical in almost every way) does not have that cooling duct which suggests it's just a precaution. That being said, I'm not sure if it had the option of the larger battery which accompanies Volvo's Premium Audio sound system.
 
#5 ·
Interesting...

I sort of assumed it had something to do with heat from the turbo, but I really don't know. This is my first turbo car, and in 30 years of working on a bunch of random cars I've never seen a duct like this before. I generally assume a method to the madness, but I realize automotive design is a bit of a progressive revelation.

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#6 ·
It has to do with flammable hydrogen being released from a battery while charging - it needs venting or a spark can make it boom. The battery has a sensor below it that dictates charging performance based on temperature.

Typically this only happens to the extent where an explosion is a worry when you overcharge the battery for a traditional SLA guy, however there is a reason the DOT says only special batteries can be inside the car, and even then they have to be vented to the outside of the car still. I guess there is still SOME risk of bad things.
 
#7 ·
The battery has a sensor below it that dictates charging performance based on temperature.
Only the earlier years. The sensor is deleted in (IIRC) late 2006.

I'd recommend finding a replacement cover, especially for the large battery (premium audio) in the photo. The others are smaller and provide air space.
 
#8 ·
Lead acid batteries need to be charged at different voltages depending on the battery temperature. At cold temperatures the battery could be charged at 15+v. At high temperatures the voltage must be 14v or lower. The ECU should have a sensor that measures or infers the battery temperature and it will adjust the charge voltage accordingly.

If the duct work was figured into the battery charging scheme, it needs to be installed... especially in hot climates. This will help prevent the ECU overcharging the battery when it expects the battery temperature to be controlled due to the duct. However I doubt the duct system is that important because it won't cool the battery in a hot engine bay very much in 90+ degree ambient temperatures.

But if it was my car I would make sure everything is installed per the original design.
 
#9 ·
Heat will reduce a battery's longevity. If a lead acid battery last longer, it is less lead going into wast in the environment. Volvo seems to take battery temperature seriously. Even the previous generation S40 had a foam cover over the battery.
 
#11 ·
Took mine out years ago to fit my intake and I’ve noticed zero difference in battery performance one way or the other. My two cents


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#12 ·
Took mine out years ago to fit my intake and I've noticed zero difference in battery performance one way or the other. My two cents

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This reinforces the theory of the duct is for pushing the battery gasses out of the battery box with ram air to not let them build up. Basically to dilute those gasses.

Cooling, if there is any, would be a side effect.

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#13 ·
I upgraded to a AGM 94R but forgot that I needed different battery terminals. I've been running without the plastic cap for the summer and haven't run into any issues (yet). At least I can have the lights on for more than 5 minutes now.
 
#15 ·
High speed electric fans for force induction battery cooling......yeah....that's it. Lol

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