A battery operated grease gun comprising: a body able to be connected to a container configured to store grease, the body defining first and second elongate chambers (6, 7) therein, the first chamber extending along a first axis and the second chamber extending along a second axis, the first axis being spaced from the second axis; first and second pistons (8, 9), the first piston configured to reciprocate within the first chamber along the first axis and the second piston configured to reciprocate within the second chamber along the second axis; a common grease channel, the common grease channel being disposed between the container and the first and second chambers (6, 7) such that the grease is able to flow from the container into the first and second chambers (6, 7); an actuator connected to the body and moveable between a retracted position, whereby grease is able to flow through the common grease channel, and an engaged position, whereby grease is restricted from flowing through the common grease channel, the actuator being configured to cause reciprocation of the first piston and the second piston when moved between the engaged and retracted positions; a grease outlet fluidically connected to the first and second chambers (6, 7) that allows for grease to be discharged from the grease gun; characterized by the second chamber having a smaller cross-sectional area than the first chamber; the second piston having a smaller cross-sectional area than the first piston; a first pressure relief channel that fluidically connects the first chamber to the container; a first pressure relief valve disposed within the first pressure relief channel, the first pressure relief valve being configured to open and thereby allow grease to flow from the first chamber to the container when the pressure in the first chamber is at or above a predetermined pressure; a first monitoring channel spaced from the first pressure relief channel; a connecting channel that fluidically connects the first monitoring channel to the first pressure relief channel; and a first monitoring spool disposed within the first monitoring channel, the first monitoring spool being configured to translate within the first monitoring channel along a longitudinal axis of the first monitoring channel between a closed and open position, wherein when the first monitoring spool is in the open position, grease is able to flow from the first chamber to the container via the connecting channel. a body able to be connected to a container configured to store grease, the body defining first and second elongate chambers (6, 7) therein, the first chamber extending along a first axis and the second chamber extending along a second axis, the first axis being spaced from the second axis; first and second pistons (8, 9), the first piston configured to reciprocate within the first chamber along the first axis and the second piston configured to reciprocate within the second chamber along the second axis; a common grease channel, the common grease channel being disposed between the container and the first and second chambers (6, 7) such that the grease is able to flow from the container into the first and second chambers (6, 7); an actuator connected to the body and moveable between a retracted position, whereby grease is able to flow through the common grease channel, and an engaged position, whereby grease is restricted from flowing through the common grease channel, the actuator being configured to cause reciprocation of the first piston and the second piston when moved between the engaged and retracted positions; a grease outlet fluidically connected to the first and second chambers (6, 7) that allows for grease to be discharged from the grease gun; the second chamber having a smaller cross-sectional area than the first chamber; the second piston having a smaller cross-sectional area than the first piston; a first pressure relief channel that fluidically connects the first chamber to the container; a first pressure relief valve disposed within the first pressure relief channel, the first pressure relief valve being configured to open and thereby allow grease to flow from the first chamber to the container when the pressure in the first chamber is at or above a predetermined pressure; a first monitoring channel spaced from the first pressure relief channel; a connecting channel that fluidically connects the first monitoring channel to the first pressure relief channel; and a first monitoring spool disposed within the first monitoring channel, the first monitoring spool being configured to translate within the first monitoring channel along a longitudinal axis of the first monitoring channel between a closed and open position, wherein when the first monitoring spool is in the open position, grease is able to flow from the first chamber to the container via the connecting channel.