Explanation: Maintenance-free lead-acid gel type batteries (D) are highly susceptible to damage from overcharging, particularly excessive voltage. Their electrolyte is a gelled sulfuric acid, which can form gas bubbles and separate if charged too aggressively or at too high a voltage. This can permanently reduce capacity and shorten battery life. A GMDSS compliant charger often has a "high (full) charging mode" designed for standard flooded lead-acid batteries (B), which can tolerate, and sometimes benefit from, higher voltages to ensure a full charge and prevent sulfation. Applying this higher voltage mode to gel batteries can cause irreversible damage to the gel structure. Therefore, this mode must be disabled or adjusted during setup to prevent harm. Ni-Cadmium (A) and Lithium-ion (C) batteries have entirely different charging characteristics and would typically require a charger specifically designed for their chemistry, rather than just disabling a high charge mode on a lead-acid charger.