I am posting this question in both the General Discussion and the Technology and Operations lists, so please excuse the redundancy.

My question is in regards to the underwater environment of U-boat wrecks that are dived often, such as the U-352 off North Carolina or the U-260 off Ireland.

In reading about the scuttling of several U-boats, one recurring obstacles for the Allied boarding parties attempting to capture a boat was the presence of toxic fumes (Chloride Gas?) created by the sea water mixing with the acid from the batteries. Given that the pressure hull of many of the U-boats is still generally intact and that water flow is restricted through the vessel, is there still a high level of acidity in or around the boats being dived today and what effect is that having on the corrosion of the boats?

Also, exactly how much acid was stored in the batteries and in other containers?