Disclosed is a modular spill containment rail system for containing a hazardous spilled substance from at least one battery. The system has a plurality of containment rails that are connectable to one another to define a perimeter around the battery. Each rail has at least one wall with a first end and a second end. At least one male connection device orthogonally protrudes from the first end and at least one female opening may be provided in the second end. A first end of a first rail may be removably received within a second end of second rail. Upon connecting the rails, at least a part of the first end of the first rail may be in an overlapping relationship with the second end of the second rail. A method for assembling a system and a containment system with a flexible liner and a neutralizing material are also disclosed herein.