"And, as I understand it, if a battery has been left for a long period of time and allowed to get very low in charge, when you try to charge that battery again it produces a lot more gas than when you try to charge a newer, fresher battery with a higher charge. I am not 100% certain of that, but I can check if anyone is interested." Absolutely correct, quite simply because if the battery has little charge (it is sulfated), then you have more lead sulfate and water to push back to the reactant side of the equation. The more molecules are there to react, in this case water in particular, the more you get out (more H2 is produced). James