Two absorptive glass mat (AGM) valve-regulated lead-acid batteries with concentration and saturation stratification were simulated. Results indicate that the concentration stratification makes the active mass (AM) in lower part discharge deeply, which results in more irreversible sulphate on the negative plate because of inefficient recharge. In saturation stratification, more AM is also discharged in lower part, but the high oxygen recombination and undercharge in the upper part of the negative plate also leads to its sulphation. When the battery is in short-time rest state, the self-charge process occurs in the upper part and self-discharge process in the lower part of the same plate, but the processes differs with rest continuing. All these make the negative plate sulphation.