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.　(c)　2007　Elsevier　Ltd.　All　rights　reserved.