Multi walled carbon nanotubes (MWCNTs) with their highly ordered structures, high electrical and mechanical stability are considered as promising and effective additives towards improving the performance of lead acid batteries (LAB) especially under high rate partial state of charge conditions (HRPSoC). In this work, carbon nanotubes with different diameter range (MWCNT 1 with diameter >50 nm, MWCNT 2 with diameter 15–50 nm and MWCNT 3 with diameter 110–170 nm) are employed as negative active material (NAM) additives in lead acid batteries operating under HRPSoC cycling conditions. The MWCNTs and NAM (containing MWCNTs) are characterized using various physical and electrochemical techniques. Correlation between key physical parameters (including surface area, dimension and structural defects) and cycle life are investigated. The results show that MWCNTs 1 with high capacitance, surface defects and display best performance regarding specific capacity and cyclability. Incorporation of MWCNT 1 ensures easy access of ions, low polarization and low solution/charge transfer resistance for the NAM. The present study indicates that MWCNT capable of improving the capacitance, conductivity and decreasing the polarization of the electrode is highly beneficial towards improving the cycle life of the lead acid batteries especially operating at HRPSoC cycling conditions.