Clean battery bank tops

I have a bank of T-105's at approx. 705amh just by slip my voltage meter touch the top of my somewhat dirty batteries and provided a reading quite to my surprise. My question is this: being that the meter obtained a reading am I loosing voltage through the tops of the bank because they are not clean, and , what is the best method of cleaning them. Should I disconnect all six and place them outside of their box and just hose them off. Or, can I place outside of their box and with the caps securely closed lightly sprinkle some baking soda over them and then hose them off or could this cause a problem. I keep up on the terminals and have all connections coated with dielectric grease connection to connection. So what would be the best method for cleaning the tops of my bank and preferably without disconnecting and removing them from their box. Thanks guys.

It's one of those natural facts about batteries. Yes, there is a mysterious 'something' escaping from the batteries. It then deposits itself on the terminals, on the tops of the batteries, and etches holes in your clothes.

It is most likely a gas of the sulfur oxide family, given off by the sulfuric acid inside the battery. Outside, it combines with water in the air, turning back into sulfuric acid. It deposits itself in a thin layer on surfaces.

It conducts electricity. There is a likelihood it steals a few mA from your battery cells.

Baking soda solution is commonly used to neutralize it. Take care not to let any drop into the cells, because it weakens the acid concentration.

Do not hose them down. Just use a piece of tissue and wipe the muck off. Its a good time to inspect the terminals and check their tightness.
Frank