Explanation: Gel cell batteries are a type of Valve Regulated Lead Acid (VRLA) battery where the sulfuric acid electrolyte is mixed with fumed silica to form a thick, paste-like gel. Because they are sealed, gas recombination happens internally, preventing electrolyte loss. This sealed nature and gelled electrolyte are critical. Unlike flooded lead-acid batteries, gel cells cannot have water added to them if overcharged. They are highly sensitive to overcharging and excessive heat, which can cause permanent damage by creating gas pockets in the gel. Therefore, special chargers designed for gel cells, often with specific voltage and current limits (e.g., constant voltage, lower float voltages), are required to ensure their longevity and performance. Options B and C are incorrect because gel cells are a type of lead-acid battery, not NICAD (Nickel-Cadmium). Option D is incorrect because gel cells have a gelled, not liquid, electrolyte and require specific lead-acid charging rates, not NICAD rates.