Battery　energy　storage　systems　(BESSs)　are　important　for　the　operation　and　optimisation　of　the　islanded　microgrid　(MG).However,　the　BESSs　will　have　different　dynamics　due　to　the　differences　in　characteristics　and　operating　conditions,　leading　to　unbalanced　state-of-charges　(SoCs).　On　the　other　hand,　because　of　the　unequal　line　impedances,　the　conventional　reactive　power-voltage　(Q-V)　droop　control　results　in　disproportional　reactivepower-sharing.　To　deal　with　suchissues,　a　power　-　frequency　(P-f)　droop-based　decentralised　SoC　balancing　strategy　is　developed　first　to　regulate　the　active　power　outputs　of　BESSs　in　terms　of　SoCs,　thus　ensuring　SoC　balancing　among　BESSs.　Furthermore,　the　authors　develop　a　Q-V　droop-based　decentralised　reactive　power-sharing　strategy　to　dispatch　the　reactive　power　among　BESSs　in　terms　of　their　respective　reactive　power　ratings.　In　this　way,　compared　with　the　existing　control　strategies,　the　proposed　control　method　is　fully　decentralised,　which　removes　the　necessity　for　both　the　central　controller　and　communication　links.　Moreover,　the　proposed　control　method　has　a　simpler　control　structure　with　the　plug　and　play　capability.　Finally,　the　simulation　results　are　presented　in　an　islanded　MG　to　demonstrate　the　effectiveness,　plug　and　play　capability　of　the　proposed　control　method.　©　The　Institution　of　Engineering　and　Technology　2020.