A fuel cell stack comprising: a unit cell block comprising a plurality of essentially planar fuel cells stacked in series wherein the unit cell block has first and second ends (2a, 2b); first and second end-plates (3, 4) opposing the first and second ends (2a, 2b) of the unit cell block respectively wherein: the first and second end-plates (3, 4) are connected together at a fixed distance apart; and the first end-plate serves as a compression surface for the first end of the unit cell block; a compression plate between the second end of the unit cell block and the second end-plate wherein the compression plate serves as a compression surface for the second end of the unit cell block; and a compression assembly urging the compression plate away from the second end-plate thereby applying a load to the second end of the unit cell block by the compression plate; the second end-plate comprises an opening for the compression assembly; characterized in that: the compression assembly is located in the opening in the second end-plate and comprises: a spring cap attached to the opening in the second end-plate, wherein the spring cap comprises an inner shoulder; a load cell button for engagement with a load cell, wherein the load cell button is located between the spring cap and the compression plate and is slidable therebetween in the stack direction z, and wherein the inner shoulder of the spring cap acts as a stop for the load cell button; and a spring assembly located between and engaging with the compression plate and the load cell button at opposite ends of the spring assembly; wherein a first load is applied to the second end of the unit cell block by the spring cap, the load cell button, the spring assembly, and the compression plate. a unit cell block comprising a plurality of essentially planar fuel cells stacked in series wherein the unit cell block has first and second ends (2a, 2b); first and second end-plates (3, 4) opposing the first and second ends (2a, 2b) of the unit cell block respectively wherein: the first and second end-plates (3, 4) are connected together at a fixed distance apart; and the first end-plate serves as a compression surface for the first end of the unit cell block; the first and second end-plates (3, 4) are connected together at a fixed distance apart; and the first end-plate serves as a compression surface for the first end of the unit cell block; a compression plate between the second end of the unit cell block and the second end-plate wherein the compression plate serves as a compression surface for the second end of the unit cell block; and a compression assembly urging the compression plate away from the second end-plate thereby applying a load to the second end of the unit cell block by the compression plate; the second end-plate comprises an opening for the compression assembly; characterized in that: the compression assembly is located in the opening in the second end-plate and comprises: a spring cap attached to the opening in the second end-plate, wherein the spring cap comprises an inner shoulder; a load cell button for engagement with a load cell, wherein the load cell button is located between the spring cap and the compression plate and is slidable therebetween in the stack direction z, and wherein the inner shoulder of the spring cap acts as a stop for the load cell button; and a spring assembly located between and engaging with the compression plate and the load cell button at opposite ends of the spring assembly; the compression assembly is located in the opening in the second end-plate and comprises: a spring cap attached to the opening in the second end-plate, wherein the spring cap comprises an inner shoulder; a load cell button for engagement with a load cell, wherein the load cell button is located between the spring cap and the compression plate and is slidable therebetween in the stack direction z, and wherein the inner shoulder of the spring cap acts as a stop for the load cell button; and a spring assembly located between and engaging with the compression plate and the load cell button at opposite ends of the spring assembly; a spring cap attached to the opening in the second end-plate, wherein the spring cap comprises an inner shoulder; a load cell button for engagement with a load cell, wherein the load cell button is located between the spring cap and the compression plate and is slidable therebetween in the stack direction z, and wherein the inner shoulder of the spring cap acts as a stop for the load cell button; and a spring assembly located between and engaging with the compression plate and the load cell button at opposite ends of the spring assembly; wherein a first load is applied to the second end of the unit cell block by the spring cap, the load cell button, the spring assembly, and the compression plate.