Battery system and method for monitoring a charge of at least one rechargeable battery

The battery system has a rechargeable battery (10) that includes several energy storage modules (11-1,11-2) having control units (12) which are connected to a network (20). The control units of energy storage modules are connected to each other in master-master system architecture within the network. The network is comprised with a bus system (21) for connection to the energy storage modules. An independent claim is included for method for monitoring state of charge (SOC) of rechargeable battery of battery system.