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DANGER: Using a Wet Cell(flooded) direct vented to atmosphere lead-acid Battery Bank "The Rules"

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More than 4 Flooded lead acid vented to atmosphere batteries is no longer an injuring life threatening explosion, IT IS "A BOMB"!

Whether 2v or 12v accumulators, using a wet cell battery (non sealed - vented to atmosphere) is extremely dangerous!

The basic rules - No fires! Garbage Incinerator, indoor wood hearth, wood barbecue, wood fuel range cooker, pot belly stove, leaves e.t.c. EVER!

Always use gas,oil or electric heaters and cookers!

Flooded lead acid vented to atmosphere system is not for fools or lazy!

In the past few years in Australia, a quantity of suburban dwellings have been destroyed in explosions by fools thinking they can sensibly house wet cell (flooded) direct vented to atmosphere off grid batteries in things such as garages or as silly, in their house!
Totally sealed batteries such as AGM and GEL-lead crystal or totally sealed wet cell lead acid would be fine, but unfortunately they cost twice as much as "wet cell ventilated to atmosphere batteries that quickly create an explosive poisonous atmosphere during use or charging".

When wet cell batteries discharge or charge they give of an extremely flammable , mildly poisonous explosive gas called "Hydrogen" that is generated by the chemical reaction of oxidizing the lead plate from the acid salts causing water to have its Oxygen atom split from its' hydrogen atoms.

There are rules to using and maintaining a wet cell battery bank system.
Why? wet cell flooded lead acid are used is because they are cheaper and last longer over a much larger DOD use to discharge quantities.
Sealed and Gel life span last up to 15 years max and generally a small DOD to number of discharges quantity.
Flooded wet cell lead acid can be made to extreme greater difference. see following "example" specs.

Link: 500ah flooded wet cell 2v accumulator adv.

Link: 12v 100ah accumulator - dry charged - flooded lead acid [NOTE: Correct use and maintenance of this can give 15 - 20 years life span - (domestic requires 12v 5000ah to 6000ah " size quantified @12v ampere")]
NOTE: I am told this battery has a valve relief system so it does not produce much explosive atmosphere each discharge action(higher pressure causes minimal evaporation), but remember it does have that risk and requires the ventilation system mentioned below!
WARNING! Because the valve system pressure must be relieved when the battery electrolyte level is topped up as maintenance, each cell stopper cap relieving gives out explosive gas while the water adding task is done, so be vigilant of others approaching during this process that requires around 1 and 1/2 hours to complete for around 480 individual cells!

1. Bank housing is outside of a dwelling and must be(compulsory - mandatory) at least 10 meters from it , (it is not allowed to be within or near any residence or building not specifically designed for "solely housing the wet cell vented to atmosphere battery bank"). The risk of injury, explosion or poisoning is "too real" to allow close proximity to living areas.

2. Because the charge controller(s) must be housed with the battery's there must be separate sealed wall compartment directly backing the battery bank to prevent gasses reaching the controller(s), but allow heat and temperature changes to progress quickly through the wall to the chargers(sealed inner sanctum). The chargers themselves must be kept dry but well ventilated (makes this a bit wobbly as a temperature incubation action for its environment so will only ever be somewhere around the required temperature). The charger must be kept well ventilated to prevent its dump load resistor being too hot(if the dump load resistor is built in with the charger).
Note: The batteries and charger housing must be kept as free from flooding by rain water run-off. Choose the location of the housing sensibly, potentially build a special (raised up on legs) non flexing base to hold the 1.5 - 2 tonne of batteries required!

3. The Battery Bank housing(inner) is totally sealed with a special 8 meter (minimum) ventilator tower that has an Air-IN(narrower) tube and an Air-OUT(wider) tube from the battery bank atmosphere.
[***] The air space(volume)inside the inner housing must be as little as possible to help the two ventilator hoses to carry away the hydrogen gas produced by usage and charging.
There should be enough space for each of the lines of batteries with a 2cm spacing between each battery and the 10L sealed water-heating drum(contains a fish tank heater for winter and late autumn early spring). The lines' ends should be half a battery forward or back from each to allow viewing on the side of each battery through the 2cm gap.
The inner housing at one corner has the "air venting outlet(ATMOSPHERE AIR OUT) hose end protruding into the housing at the top" only a few centimeters in.
The opposite corner of the inner housing has the inlet(ATMOSPHERE AIR IN) hose protruding in with its collection orifice end only a few centimeters from the floor.

This means that with very little inner housing internal space and very low air speed past the outlet nozzles of the two hoses the hydrogen will be removed AND, if there were to be any ignition of any remaining hydrogen in the confined space(or outside), such an explosion would be unlikely to ever be of any severity! (and ventilating by running long distances of tube with a fan are not required).

One final note, always put a few totally 180o "S"-bend(kinks - do not crush closed) into both hoses up the pole a meter or so before the nozzle(hose end) outlet, and again another before the inner housing connection. This is to stop the force of any direct blast back down the hose.

* Clean hoses of spiders and alike regularly by taking them down and running water through them.

4. Electrolyte levels(sulfuric acid solution) in each battery must be checked at least once per week, there will be a marker on the transparent battery casing showing the upper and lower allowed levels for proper operation.
NOTE: It requires around 1 and 1/2 hours to read and top up 480 individual cells with distilled water, it's dangerous because of the electrical power voltage and source present, the battery housing requires design with some extra space so the upper and lower electrolyte markers can be seen easily and effectively safely.

5. No naked flame or smoking or electrical work to be within 10 meters of the battery bank housing.

6. Before opening the battery bank door "all flammables or possible flammable triggers must been removed from the vicinity"
e.g. petrol cans empty or full, kerosene, solvent containers, LPG gas bottles, lighters, matches, burners or solderers, candles, lamps(using a fully waterproof torch is a good idea!), running vehicles, electric motors - quad-copters, blacksmithing fires e.t.c..

7. After opening the battery bank door, the housing must be leaved open for 10 minutes prior to commencing any actions within it, near it, or upon it to clear the explosive hydrogen gas build up occurred from its' charging and use.

8. The temperature shielding from sunlight by three non contacting ventilated wall sets (See: "Ensuring battery service life")(lids with the corners slotted - grooved through 1cm to allow air flow) and basic continuous 20o Celsius environment of the batteries is much the same as sealed battery environment control, except the inner most wall set are totally/completely sealed sealed and ventilation is done by the two tubes extended to the top of the ventilation tower (8M high)!

9. The inner door/housing-cover must be fastened tight non moving(no rattle or looseness) and sealed, but one more item - locked! to prevent tamper by children, and the ventilation tower and its' tubes must not be tamper-able or climbable either!

10. Read the manufacturers sulfuric acid solution percentage information for the batteries and use the correct solution percentage.

11. Use only distilled water to top up each battery cell. You can easily make a still using a clean unused 20L plastic drum-canister and around 10 meters of plastic fish-tank-tube sealed into the pouring hole of the 20L drum, by placing the drum full of rain-water in the sun and running the tube up to roof level and dangling the remainder in a coiled ball down around a pole in the shade(do not allow sunlight to get to the collector) into a clean drum never used for anything except distilled water.

12. One final action needs to occur as maintenance on flooded wet cell lead acid batteries. A process called "equalizing" is required to occur around once every three months or as recommended by the manufacturer for the model specification. Equalizing is a process of lifting the battery voltage to heavy state of over-voltage deliberately to excite or re-excite the batteries chemically.

An easy way to make a ventilation system is the same principle of putting your wind turbine higher, the air has tendency to move a little faster higher in altitude. Seal one end of some hose material into the inner battery bank compartment and take its length to the top at 8M and bend it over in a hook shape with 5 inches to the end pointing down to prevent rain entering it.
Then seal a second hose into the inner battery bank compartment and put it up 5M and bend the end over with 5 inches pointing down.
The faster air at 8M will have the tendency to draw the air by Venturi effect out the higher end hose. To make this operate better, find a thick plastic washer with an inner hole half the diameter of the hoses' inner hole diameter and glue it over the top end of the shorter input hose. This will cause it to be much more favorable to leave out by the upper long hose end!

The only other method is to run the two tubes(one inlet one outlet - with small continuous blower extractor fan out there 100 meters away also) underground to 100 meters away and up a three/four meter mast.(keep the inlet outlet orifice points apart at least 1 meter)

Some links if you want....