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I'd like to experiment with running a small server (5.5 watts) / 85AH deep cycle battery / charged via 30 watt solar panel from my bedroom.

I generally keep the window open, but want to make sure it's relatively safe for me to keep the battery inside and out of the sun. I hear the recharge process can release fumes which, if concentrated in a small area, can be toxic, but want to know if discharging also creates fumes and, in either case, if keeping the window open is preventative enough to prevent a build up.

Thanks for your response.

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Not "safe" without extra care. Death unlikely but likely possible if you "just do it".

Can be made "safe"

Discharge will not release 'fumes' in general use.

Risk from "gassing" (Gargoyle knows) can be kept small but not zero when charging with a panel of that relative size. ie 12v say & 30 Watt = 2.5A. 24V = 1.25 A. + say 3% and 1.5% ~ of bat 1 hour rate.

Small but non zero chance of Hydrogen and sulphuric acid fumes if battery not designed to vent unless 100% sealed with full recombination control. Ventilation would be an extremely good idea.

More if required ...

Long long long ago I charged a truck battery at a moderately high rate in a small closed room where I was sleeping :-). Took many weeks for my throat and nasal linings to "recover".

Data point: Just came across this [here](http://www.vonwentzel.net/Battery/00.Glossary/ ) while looking for something else:

  • Gassing: This is a very dangerous condition that can occur if batteries are charged too fast. One of the byproducts of Gassing are Oxygen and Hydrogen. As the battery heats up, the gassing rate increases as well and it becomes increasingly likely that the Hydrogen around it will explode.
    The danger posed by high Hydrogen concentrations is one of the reasons that the American Boat and Yachting Council (ABYC) requires that batteries be installed in separate, well-ventilated areas.

  • " ... As the battery heats up, the gassing rate increases as well and it becomes increasingly likely that the Hydrogen around it will explode. The danger posed by high Hydrogen concentrations is one of the reasons that the American Boat and Yachting Council (ABYC) requires that batteries be installed in separate, well-ventilated areas." | From here | And ABYC site here

American boat and Yachting council website here
http://www.abycinc.org/

No open access data available on AYBC site - you have to be a member to read about how to be safe.

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For what it's worth, cruising yachts have banks of batteries to provide electricity when the motor's not running while sailing or docked. They can be about as good an example of an enclosed space as you can get, there are ~30' boats that have tiny cabins where a bench may function as a booth when the dinner table is folded down and a bunk at night, and if you pull the cushions off the bench you find it's also the battery locker and you've been sleeping on top of the batteries.

Marine electrical systems are no doubt designed not to poison the occupants, but ventilation is not necessarily good on a boat (they limit the number of holes, for obvious reasons), so it is apparently possible to design these systems safely and there are people who live on cruising yachts for months or years. I don't have experience designing or working on these systems, but I think they might provide a good example to follow.

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  • \$\begingroup\$ Thanks for the response Suboptimus. Though, I just read up on this today and the batteries on boats and yachts are usually sealed AGM batteries that give off no fumes (unless overloaded). This makes sense due to the rocking nature of the boat and how unsealed lead-acid batteries might be unsafe in that enviornment. \$\endgroup\$
    – Mauvis Ledford
    Dec 10, 2011 at 0:38
  • \$\begingroup\$ Just came across this : " ... As the battery heats up, the gassing rate increases as well and it becomes increasingly likely that the Hydrogen around it will explode. The danger posed by high Hydrogen concentrations is one of the reasons that the American Boat and Yachting Council (ABYC) requires that batteries be installed in separate, well-ventilated areas." | From here | And ABYC site here \$\endgroup\$
    – Russell McMahon ♦
    Dec 13, 2011 at 23:42
  • \$\begingroup\$ Interesting find. I can say that superficially boat battery compartments don't look well-ventilated at all, so they must use active ventilation systems (i.e., fans) to exhaust the fumes. It would probably be useful to OP to research how those ventilation systems are designed. \$\endgroup\$
    – Suboptimus
    Dec 14, 2011 at 0:03
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Re: Lead acid batteries in a confined space -- Any lead acid battery which includes flooded, gel and AGM batteries, will evolve H2 and O2 if overcharged too much. Sealed batteries use recombinant technology but are valve regulated, meaning that they will vent if the internal pressure exceeds the set pressure. Some batteries have captured vents that can be hooked up to a line to the outside and safely vented.

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Unless you overcharge the battery, the amount of hydrogen and oxygen released is very low. Also, it's not particularly harmful compared to many other gases. To actually release any sulphuric acid fumes, you have to supply very high voltage and you will detect the smell immediately. Can you use a proper battery regulator that keeps 14.4 V or less for a 12 V battery (13.6 V for UPS long term float voltage is common for a reason), and a sealed battery? I would personally have no problem having that under my bed.

Source: electronic engineer, have designed commercial lead-acid battery chargers for five years.

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It is perfectly fine to keep a AGM/GEL battery in a living space, as long as you make sure that a short circuit will not happen. AGM/GEL batteries do not vent during charging or discharging, they still might vent if you short them for a not so short period of time.

I keep one AGM and one gel battery in my bedroom for "emergency" backup.

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Charging in a closed room is very dangerous because of the gas coming out from the battery. If sparks may occur the battery will explode. I've made a battery charger that can charge ten batteries or more simultaneously. Sometimes I did overnight charging in a well ventilated area. I've never experienced a battery explosion.

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