A charging system for autonomous transport vehicles in a warehouse storage and retrieval system, the charging system comprises: at least one charging contact disposed on each pick floor level of the storage and retrieval system where the total number of charging contacts of the charging system is at least two, each of the charging contacts being located at a transfer station (290T1, 290T2); and at least one power supply configured to supply power to the charging contacts; characterized in that: a first controller which is in communication with each transfer station (290T1, 290T2) and each autonomous transport vehicle, the first controller is configured to: communicate information relating to a transfer of items between a transfer station (290T1, 290T2) and a predetermined one of the autonomous transport vehicles to apply power, via the control of the power supply, to the at least one charging contact for charging the predetermined autonomous transport vehicle corresponding to the transfer and located at the transfer station (290T1, 290T2), to supply power to the charging contacts for charging the predetermined autonomous transport vehicle simultaneously with the predetermined autonomous transport vehicle exchanging items related to the transfer at the transfer station (290T1, 290T2), and to synchronize the predetermined autonomous transport vehicle ingress and egress to/from the charging contacts with other autonomous transport vehicles destined for, leaving, or charging at the charging contacts to maximize substantially full utility of the charging contacts. at least one charging contact disposed on each pick floor level of the storage and retrieval system where the total number of charging contacts of the charging system is at least two, each of the charging contacts being located at a transfer station (290T1, 290T2); and at least one power supply configured to supply power to the charging contacts; characterized in that: a first controller which is in communication with each transfer station (290T1, 290T2) and each autonomous transport vehicle, the first controller is configured to: communicate information relating to a transfer of items between a transfer station (290T1, 290T2) and a predetermined one of the autonomous transport vehicles to apply power, via the control of the power supply, to the at least one charging contact for charging the predetermined autonomous transport vehicle corresponding to the transfer and located at the transfer station (290T1, 290T2), to supply power to the charging contacts for charging the predetermined autonomous transport vehicle simultaneously with the predetermined autonomous transport vehicle exchanging items related to the transfer at the transfer station (290T1, 290T2), and to synchronize the predetermined autonomous transport vehicle ingress and egress to/from the charging contacts with other autonomous transport vehicles destined for, leaving, or charging at the charging contacts to maximize substantially full utility of the charging contacts. communicate information relating to a transfer of items between a transfer station (290T1, 290T2) and a predetermined one of the autonomous transport vehicles to apply power, via the control of the power supply, to the at least one charging contact for charging the predetermined autonomous transport vehicle corresponding to the transfer and located at the transfer station (290T1, 290T2), to supply power to the charging contacts for charging the predetermined autonomous transport vehicle simultaneously with the predetermined autonomous transport vehicle exchanging items related to the transfer at the transfer station (290T1, 290T2), and to synchronize the predetermined autonomous transport vehicle ingress and egress to/from the charging contacts with other autonomous transport vehicles destined for, leaving, or charging at the charging contacts to maximize substantially full utility of the charging contacts.