Making a DIY battery box - couple questions

[larry2c]

I want to upgrade the batteries on our TT and one of the options I am considering is to go with 2 group 29 batteries. They would fit in the existing battery box with a bit of room to spare but not enough room for any of the commercial battery boxes I've seen. I found a DIY box made from plywood and it looks like it would be perfect for my needs (link to RV.net forum).

My question is, with flooded batteries, do I need to provide some ventilation? The person who did the project has an elbow in the side of the box for the wires to come out but that seems like a small amount of ventilation. Also, the box in the thread supposedly has some foam lining to help with vibration. My space will be tight, how much padding would be needed - if any?

Any thoughts on doing this right would be appreciated!

[A32Deuce]

Yes they need ventilation also securely mounted. No padding needed.

[babock]

If you have just one hole for wires and it's near the top of the box, that is fine.

[larry2c]

Thanks - that makes the build a bit easier!

[markb422]

AGM batteries need no ventilation.

[A32Deuce]

That is true, but he said flooded batteries. AGM can also be mounted any way other then upside down.

[Splitshaft]

Actually, AGM batteries do need a vent. While the vent would not likely be used, AGM batteries use recombinant technology and they can vent if over charged as they are not 100-percent sealed. The gases, contained, can make for a very explosive environment.

[larry2c]

Originally Posted by Splitshaft

Actually, AGM batteries do need a vent. While the vent would not likely be used, AGM batteries use recombinant technology and they can vent if over charged as they are not 100-percent sealed. The gases, contained, can make for a very explosive environment.

Interesting I'd never heard that before - thanks for the info.

[A32Deuce]

I have had one in a trunk for 18 years.

[TitanMike]

If you use a wooden box it would be a good idea to seal the wood well with a chemical resistant paint. While the primary product produced by a charging battery is Hydrogen (which will vent through small holes near the top of the box very nicely), under warm conditions the gases can also contain water vapor and droplets of sulfuric acid. This will cause a wood box to deteriorate rapidly.


As a side note, I have two group 29 (Interstate SRM-29) batteries on my trailer and they fit in a Group 27 size box nice and snug. I will be changing to GC-2 6 V batteries at the end of this season as the group 29 12 V batteries are not holding up well under my needs. I have a Victron battery monitor and never allow state of charge to go below 50% but as I monitor my specific gravity readings they are dropping and cell to cell variations are rising. In short, the SRM-29's are a poor choice for any application when they are being used as a true Deep Cycle. Two GC-2's will provide almost exactly the same total amp hour capacity as the two 12 V batteries but will handle the deep cycling much better for much longer. Mine will be two years old (by date of manufacture) at the end of this year. Not very good.