Yes, even Nicads have water (a water\dissolved salt electrolyte, actually) in them. Large Nicads (we had 'em on some merchant ships) have a Potassium Hydroxide solution as the electrolyte and they will electrolyse water (turn it into gaseous hydrogen and oxygen) if overcharged, leading to a need to top up with distilled water. . .. .So what's the difference between these and the good old lead-acid we all know so well from our cars etc?. .. .First, the electrolyte is a strong alkaline one, not acidic. It'll still burn you though, and the stuff is very corrosive so don't get it splashed onto anything/anyone you care about.. .. .Second, unlike lead-acid cells, the specific gravity of a Nicad's electrolyte changes little throughout the charge-discharge cycle so measuring it doesn't tell you where you are on the discharge curve.. .. .They are a very efficient energy storage medium on a cost-per-unit-weight basis, but require specialist care if they are to give maximum service life. Treat them with care! If in doubt about them, seek out a battery technician and ask his expert advice. They will be happy to be asked and tell you all you need to know.