A method of operating a first battery server for use with a first node of a power interchange system that distributes direct current power between a plurality of nodes, wherein each node of the plurality of nodes comprises a storage battery to store electrical energy and a battery server to control transmission of DC power from the storage battery of the node to one or more other nodes and to control receipt of DC power at the node from one or more storage batteries (160b,...) of one or more other nodes, wherein the method comprises: monitoring a state of charge in a first storage battery of the first node and a usage rate of power by one or more electrical components of the first node; and in response to detecting that the state of charge of the first storage battery and/or the usage rate of power satisfies one or more conditions, requesting that a master node of the power interchange system controls transmission of power from another node of the plurality of nodes to the first node, characterized in that the master node is one of the plurality of nodes, so that only the battery server of the master node has the right to control the transmission and reception of DC power to and from the nodes and a battery server having no control right is prevented from performing the DC power transmission and reception without permission or instruction, and wherein requesting that the master node controls transmission of power from another node to the first node comprises, in a case that the first node is the master node, controlling transmission of power from another node to the first node, and wherein the method further comprises operating the first battery server of the first node to carry out an act of: in response to determining that power is not presently being shared between nodes of the plurality of nodes and no node is currently requesting receipt of power from one or more other nodes of the plurality of nodes, configuring the first node to no longer act as the master node, and wherein the method further comprises operating the first battery server of the first node to carry out an act of: in response to determining that no node is currently acting as the master node, arbitrating between the plurality of nodes which node will act as the master node. monitoring a state of charge in a first storage battery of the first node and a usage rate of power by one or more electrical components of the first node; and in response to detecting that the state of charge of the first storage battery and/or the usage rate of power satisfies one or more conditions, requesting that a master node of the power interchange system controls transmission of power from another node of the plurality of nodes to the first node, characterized in that the master node is one of the plurality of nodes, so that only the battery server of the master node has the right to control the transmission and reception of DC power to and from the nodes and a battery server having no control right is prevented from performing the DC power transmission and reception without permission or instruction, and wherein requesting that the master node controls transmission of power from another node to the first node comprises, in a case that the first node is the master node, controlling transmission of power from another node to the first node, and wherein the method further comprises operating the first battery server of the first node to carry out an act of: in response to determining that power is not presently being shared between nodes of the plurality of nodes and no node is currently requesting receipt of power from one or more other nodes of the plurality of nodes, configuring the first node to no longer act as the master node, and wherein the method further comprises operating the first battery server of the first node to carry out an act of: in response to determining that no node is currently acting as the master node, arbitrating between the plurality of nodes which node will act as the master node. in response to determining that power is not presently being shared between nodes of the plurality of nodes and no node is currently requesting receipt of power from one or more other nodes of the plurality of nodes, configuring the first node to no longer act as the master node, and wherein the method further comprises operating the first battery server of the first node to carry out an act of: in response to determining that no node is currently acting as the master node, arbitrating between the plurality of nodes which node will act as the master node.