openinverter forum

I'm in the process of designing my battery box. Checking the forum and wiki, it seems the general consensus is that it is better to seal the box. My climate has an annual temperature range of -5 to 40C. Is it a good idea to include some sort of pressure equalization valve and/or a drain for moisture?

Yes, and for off gassing if there’s ever a battery issue

I've done both sealed and unsealed over the years and found where moisture can't get in moisture can't get out either. So I do suggest intended venting at a spot where spray can't get in.

There are one way moisture barrier wrap materials for buildings. I'm sure someone has put these in a grommet to make a one way "moisture valve". Basically let's moisture out but not in and allows a small amount of air to flow either way.

Steve16 wrote: ↑Wed Apr 09, 2025 10:39 pm Is it a good idea to include some sort of pressure equalization valve and/or a drain for moisture?

Yes there are specific valves for this, they equalize pressure through a membrane that stops moisture ingress.

Example of such a valve on my webstore https://citini.com/product/pressure-rel ... ble-valve/

Many sizes and shapes of these valves exist, you need the pick the right one for your box size.

Thanks, I will begin looking for the best pressure equalization valve and add my findings to the wiki.

Bratitude wrote: ↑Thu Apr 10, 2025 4:51 am Yes, and for off gassing if there’s ever a battery issue

Older posts but stil relevant...

I suggest to make intentional 50mm hole or two at the battery box rear end and tape it with silver(alu) tape from both sides. It can hold normal pressure and will seal against moisture, but will rupture in case of overpressure. A sort of single use membrane...

Regarding moisture i suggest making a small hole on the bottom and use the car tire valve without rubber part so you have a tube sticking lower than the lowest part of battey floor. This way no water will go back in but rather out...

I would not rely on aluminium tape for any automotive use tbh, my experience with it is not great and the adhesive that it uses not reliable. How about a proper air tightness tape? Or some vapour variable membrane, it closes up as humidity rises. Something like Pro Clima Intello or similar.

Jacobsmess wrote: ↑Thu Jun 26, 2025 11:41 am I would not rely on aluminium tape for any automotive use tbh, my experience with it is not great and the adhesive that it uses not reliable. How about a proper air tightness tape? Or some vapour variable membrane, it closes up as humidity rises. Something like Pro Clima Intello or similar.

Tom's link above is exactly this,

tom91 wrote: ↑Thu Apr 10, 2025 11:12 am Yes there are specific valves for this, they equalize pressure through a membrane that stops moisture ingress.

Example of such a valve on my webstore https://citini.com/product/pressure-rel ... ble-valve/

I think it's an excellent price for what you get. Removes the need for the diy attempts and their huge time suck.

And Tom, it would likely help people find it if you mention something like it's a semi permeable membrane that allows airflow but rejects moisture. Yeah it's in the datasheet but I'm sure people think it's just a safety valve from the description.

What you are looking for is EPTFE, same as goretex - allows the box to breathe. ePTFE membranes in the 0.2-0.3 µm range are generally excellent for blocking moisture while still allowing air to pass through. Look on aliexpress, they come both in sticker or gland format.