ernest2,
Good question, and I'm not exactly sure how to answer it. Most 'sealed' lead acid batteries (like you find in a car) are not really 'sealed', just harder to get into (you can still add water to them). They 'slosh' when shaken, (not that I recomend shaking a battery!). The 'gel-cells' use a 'thicker' electrolyte, not water. Gel-cells are found in the 'cheaper' computer UPS's if that helps.
- 'Doc