A few quick battery box questions

[GonzoF1]

I am going to redesign our battery boxes. We are using eight 6V GC2 batteries for the house bank and three dual purpose for starting duties. They are currently in four separate boxes and I want to reduce that to just two.

- Is there a minimum spacing needed between batteries and the box sides?
- Is there a maximum number of batteries recommended per box? In this case, is six too many?
- How low, in relation to the battery's vertical sides, can a vent be? Could it, for instance, be halfway up?
- Is there a formula for the size of the vents based on the number or size of batteries needed per box?

Thanks-

 

[sail sfbay]

Came across this article that addresses many of your questions: Battery Box to keep your boat batteries safe and secure. (diy-wood-boat.com)

- Is there a minimum spacing needed between batteries and the box sides? there should be breathing space around each battery
- Is there a maximum number of batteries recommended per box? In this case, is six too many? I have seen rv battery boxes that can hold six 6v batteries Battery Box That Will Fit Four 6-Volt Batteries | etrailer.com my powerboat has a battery box for 4 6v house batteries and another with 2 12v starting batteries
- How low, in relation to the battery's vertical sides, can a vent be? Could it, for instance, be halfway up? vent from highest point on the box; to find the ventilation holes make sure the lid is on the battery box, run your finger around the lip of the lid feeling for gaps. There will most likely be one or two gaps between the cover and the body of the battery box. These are your vents.
- Is there a formula for the size of the vents based on the number or size of batteries needed per box? not that aware of, but you might use the formula for industrial battery vent flow rate in this link How to calculate battery room hydrogen ventilation requirements | Ethos Power Associates then calculate the vent size based on orifice sizing formula.

 

[dlochner]

- Is there a minimum spacing needed between batteries and the box sides?
They should not touch, more spacing is better than less. ABYC says no more than 1" movement in any direction. Heat dissipation is important, cooler batteries charge faster and last longer.

- Is there a maximum number of batteries recommended per box? In this case, is six too many?
Not that I am aware of. On a boat space limitations may be a bigger factor. Venting battery heat will be important, more batteries, more heat.

- How low, in relation to the battery's vertical sides, can a vent be? Could it, for instance, be halfway up?
Hydrogen is lighter than air, the vent must be at the highest point so that the H can escape. The H will escape from the battery caps. A lower vent will not allow the H to escape. While there are standards as @sail sfbay notes, these seem more oriented to large solar installations where many batteries will be charged every day. On a sailboat, that is less of an issue as the amount of H generated will be much lower.

- Is there a formula for the size of the vents based on the number or size of batteries needed per box?
yes, see post above.

Depending on your intended use, it might be worth considering changing chemistries. Two Group 31 Carbon Foam AGMs (Firefly) have just slightly less usable capacity than 2 GC batteries. While more expensive, they have a longer cycle life. The one drawback is charging, they require periodic high charging currents, ~.4C.

 

[GonzoF1]

- How low, in relation to the battery's vertical sides, can a vent be? Could it, for instance, be halfway up? vent from highest point on the box; to find the ventilation holes make sure the lid is on the battery box, run your finger around the lip of the lid feeling for gaps. There will most likely be one or two gaps between the cover and the body of the battery box. These are your vents.

Ok, so if I flute the top edge of the box, that would be enough? The only question I have there is that during heavy rain, water comes in the access hatch directly above it. Therefore, the tops will be overhang the top edge of the box by an inch or so. Meaning, the gas will build up in the top of the box until it overcomes that distance. Will that still provide the venting? There is no option for direct venting through the lid without compromising water ingress points.

Depending on your intended use, it might be worth considering changing chemistries. Two Group 31 Carbon Foam AGMs (Firefly) have just slightly less usable capacity than 2 GC batteries.

Maybe some other time. These GC2s are new this season. We don't push our batteries very hard, only anchoring out a few times a season. I am fine with the lower cost more often than the large upfront cost to replace them less often. FLAs are fine.

 

[sail sfbay]

If I know your flute size I will have to get my slide rule out and start making calculations. What battery box are you planning to install. That way the forum can access venting adequacy. My Hunter 46 house lead acid now AGM battery box, located under the salon floor, does not have a vent and never had an issue. Nor does the 4 6v covered battery box on my powerboat.

 

[GonzoF1]

If I know your flute size I will have to get my slide rule out and start making calculations. What battery box are you planning to install. That way the forum can access venting adequacy. My Hunter 46 house lead acid now AGM battery box, located under the salon floor, does not have a vent and never had an issue. Nor does the 4 6v covered battery box on my powerboat.

What box? I am making the boxes myself. This is a relatively open powerboat engine room. No tight quarters here. But it sounds like meeting a standard for venting just isn't there and I don't need to worry about it very much. As long as there are places for the gasses to sneak out, it sounds like it will be fine.

 

[sail sfbay]

Consider a vent at the top corners as show in the photo below for this commercially-available four (4) 6v golf cart battery box. The lid sits on top of the box with a 1 inch "lip" and has a vents.

 

[GonzoF1]

Consider a vent at the top corners as show in the photo below for this commercially-available four (4) 6v golf cart battery box. The lid sits on top of the box with a 1 inch "lip" and has a vents.

View attachment 197112

If you are considering the wire access cutouts as vents, then I don't have anything to worry about. From the overall square inches that these are compared to the size of the box (including the 1" overhang), I will have plenty of ventilation under the lids I have designed. Thanks.

 

[Bob S]

I built my own battery box for six GC batteries. Just be sure to epoxy the inside of the box so it can contain any acid spills. I fiberglassed the inside for strength and epoxied the inside and outside to seal the wood from moisture. Then I brought it to a truck shop to have it Rhino Lined per Maine Sail's advise. I made my cover with four 2" x 6" cutouts for wire access and venting on each end.