The SMF Batteries are Sealed Maintenance Free batteries, which are flat plate batteries that don't require topping off and typically don't generate any fumes or vapors continuously. The fact that these batteries require no maintenance is their main selling point. This is why they do not need to be topped off with acid or water since they are sealed. In the right circumstances, sealing makes them leakproof, so there is no need to worry about leaking battery acid or water loss during the charging cycle of our SMF Batteries