Replenishing　energy　to　wireless　sensor　networks　is　always　a　crucial　problem　as　the　energy　capacity　of　sensor　nodes　is　very　limited.　Scheduling　mobile　chargers　to　charge　sensor　nodes　has　been　widely　studied　due　to　its　efficiency　and　flexibility.　However,　most　existing　works　focus　on　maximizing　the　charging　utility　or　charging　efficiency,　which　ignores　the　task　performing　functions　of　sensor　nodes.　In　this　paper,　we　study　the　problem　of　scheduling　a　mobile　charger　to　maximize　the　task　utility　achieved　by　sensor　nodes.　We　consider　two　different　scenarios　where　sensor　nodes　are　deployed　on　a　line　road　and　a　ring　road,　respectively.　We　prove　the　NP-Hardness　of　our　problems　and　design　two　approximation　algorithms　with　guaranteed　performance.　We　also　investigate　how　to　jointly　schedule　two　mobile　chargers　in　the　line　road　scenario,　and　design　a　corresponding　approximation　algorithm　to　address　the　problem.　We　prove　the　approximation　ratio　of　our　algorithms　through　theoretical　analysis,　and　conduct　extensive　simulations　to　validate　the　performance　of　our　algorithms.　Simulation　results　show　that　our　algorithms　always　outperform　the　baselines,　which　demonstrates　the　effectiveness　of　our　algorithms.　©　2022　Elsevier　B.V.