yup, i maintain power plants for part of my job, and on any wet cell battery, water needs to be regularly checked. Especially, on a wet cell battery, where one cell is performing all the work. Most consumer batteries these days are not wet cell, or another term flooded cell. So most people do not realize that we still have wet cells in some of our cars. Usually there will be a water level line. When a battery discharges, the electrolyte level will change. Water in fact becomes the electrolyte when added, it will evaporate over time, but the acid will stay in the battery for the most part.
So it is important to keep a maintained water level in your battery.
Now on a side note, I have never had a battery that needed water. I am in a bad habit of never even checking them anymore. I couldnt even tell you what kind of battery is in my BMW. As important as it is, they just never go bad frequently enough to get out and check the battery every week, and they are very expendable, so most people are to lazy to maintain it.
Kaz said:
This depends on whether the battery is one that even has water in it. There are lots of sealed types out there these days (thought usually not used in cars from the factory) that dont use water, such as gel, spiralcells, and I believe AGM.
But if its one that has the traditional 'wet' construction and if there's any way to get in there to add water, I do it.