As others have said, it should be OK in a large room (I would not recommend a bedroom - something more like a basement) with some ventilation (window open 1 cm). It definitely should not be put inside a tightly sealed box. The main reason is explosion risk. Hydrogen is such a small molecule that it will diffuse slowly through the plastic walls of the battery and then may accumulate inside the sealed box. Any concentration >4% by volume in air is flammable. If the battery is over-charged, then it will gas much more quickly, so the hydrogen and oxygen will come out of the vents. The battery may get hot enough to boil the electrolyte, in which case you get sulfuric acid and water vapor coming out of the vents, too. If the external container were really well sealed and there were a lot of boiling, the container could burst from the pressure, but that is unlikely. Russell, you must have really over-charged that battery! I once accidentally breathed in a good whiff of sulfuric acid vapor and felt a burning sensation in my nose and sinuses, but it had no lasting effect beyond a couple of minutes. Sean On Fri, Dec 30, 2011 at 5:40 PM, V G wrote: > Quick question - does a SEALED lead acid battery need to be charged in > a ventilated area? > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .