Venting battery box?

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Apr 11, 2008
Vessel Name
Vessel Make
DeFever 48
I'm going to move my wet cell batteries from the engine room to forward under a berth and was wondering if the vent from the box should include a powered vent connected to a voltage sensative relay. Is passive venting enough? I was thinking about using a small computer fan on the intake side that would turn on around 13V to allow for venting during the charging ie: venting times. The fan would also help to keep the batteries cooler and extend their life. Should the fan just run 24/7 and avoid the relay?
I would think passive venting should be fine.* Getting the batts out of the engine room will do wonders for the temperature, so I wouldn't worry about the minor difference you'd get with a fan.* Main thing I'd think you'd want to do is to keep the odor and corrosiveness of the battery gas out of the cabin.

Goes without saying that, if you do decide to use a fan, use a brushless one (i.e. computer fan)*as sparking brushes in a hydrogen-oxygen atmosphere probably isn't a real good plan.
" Is passive venting enough?"

Plenty , unless the bat set is thousands of pounds and you can charge at 300A all day long.
Check out Hydrocaps or miser caps at The Hydrocaps will recombine gases coming out of the battery and you won't need venting. There are some compartment venting setups that come on when the charger comes on as well. The computer muffin fan is a good idea as well. I have AGM's under my berth, but don't worry about them, as they don't really vent unless they're overcharged.
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