A cordless treadmill, comprising: a frame, comprising a first side surface, a second side surface opposite the first side surface, and a bottom surface, the first side surface and the second side surface generally orthogonal to the bottom surface such that the first side surface, second surface and bottom surface define a U-shaped channel extending generally lengthwise of the cordless treadmill, the frame further comprising a plurality of openings (232, 236, 238, 240, 242, 250 252, 254, 256, 258) in the first and second side surfaces; a belt system, comprising a forward roller configured to roll on a forward axle and a rear roller configured to roll on a rear axle, the forward and rear axles extending laterally from the forward and rear rollers, respectively, such that the forward and rear axles support and allow rotation of the forward and rear rollers in the frame, and a belt placed around the forward and rear rollers, characterised in that, the treadmill further comprises a cartridge, comprising a first roller (714, 716, 718, 720, 722, 724) having a longitudinal axis that extends along a width of the frame and a second roller (714, 716, 718, 720, 722, 724) adjacent to and laterally spaced apart from the first roller, wherein a longitudinal axis of the second roller extends along the width of the frame, and wherein the longitudinal axis of the first roller and the longitudinal axis of the second roller are offset from each other by a predetermined distance, the cartridge further comprising a first collinear roller and a second collinear roller, wherein the first and second collinear rollers extend along a width of the frame and each of the first and second collinear rollers are adjacent to the first and second rollers such that the first collinear roller is on an opposite side of the first and second rollers than the second collinear roller, the cartridge further comprising at least one connecting member mounted to each of the first and second rollers and the first and second collinear rollers such that a first tab (702, 704, 706) and a second tab (702, 704, 706) extend laterally from each side of the mounted first, second, first collinear, and second collinear rollers, the cartridge configured such that the endless belt of the belt system rotates over and is supported by the cartridge; wherein the frame is adapted to receive the belt system and the cartridge as they are lowered into the frame, and wherein the frame is adapted to place the belt of the belt system into tension as the belt system is lowered into the frame. a frame, comprising a first side surface, a second side surface opposite the first side surface, and a bottom surface, the first side surface and the second side surface generally orthogonal to the bottom surface such that the first side surface, second surface and bottom surface define a U-shaped channel extending generally lengthwise of the cordless treadmill, the frame further comprising a plurality of openings (232, 236, 238, 240, 242, 250 252, 254, 256, 258) in the first and second side surfaces; a belt system, comprising a forward roller configured to roll on a forward axle and a rear roller configured to roll on a rear axle, the forward and rear axles extending laterally from the forward and rear rollers, respectively, such that the forward and rear axles support and allow rotation of the forward and rear rollers in the frame, and a belt placed around the forward and rear rollers, characterised in that, the treadmill further comprises a cartridge, comprising a first roller (714, 716, 718, 720, 722, 724) having a longitudinal axis that extends along a width of the frame and a second roller (714, 716, 718, 720, 722, 724) adjacent to and laterally spaced apart from the first roller, wherein a longitudinal axis of the second roller extends along the width of the frame, and wherein the longitudinal axis of the first roller and the longitudinal axis of the second roller are offset from each other by a predetermined distance, the cartridge further comprising a first collinear roller and a second collinear roller, wherein the first and second collinear rollers extend along a width of the frame and each of the first and second collinear rollers are adjacent to the first and second rollers such that the first collinear roller is on an opposite side of the first and second rollers than the second collinear roller, the cartridge further comprising at least one connecting member mounted to each of the first and second rollers and the first and second collinear rollers such that a first tab (702, 704, 706) and a second tab (702, 704, 706) extend laterally from each side of the mounted first, second, first collinear, and second collinear rollers, the cartridge configured such that the endless belt of the belt system rotates over and is supported by the cartridge; wherein the frame is adapted to receive the belt system and the cartridge as they are lowered into the frame, and wherein the frame is adapted to place the belt of the belt system into tension as the belt system is lowered into the frame.