NOVELTY - The method involves monitoring and recording state information of battery units (9). The state information is transmitted to a valuation service computer system at each battery unit. The state information is received from the battery units at the valuation service computer system. Hardware/software configurations is obtained for each battery unit. A transaction value is calculated for each battery unit using the state information and the hardware/software configurations for the battery unit at the valuation service computer system.    USE - Method for facilitating transactions of smart battery units between transacting participants of an electrical device e.g. electric vehicle such as electric car.    ADVANTAGE - The medium enables allowing a consumer to estimate cost of the transaction before the transaction occurs, so that the battery units can be valued periodically or daily, electric tanks can display total transactional value of the battery units and total energy stored, battery unit suppliers can display the transactional value of the battery units available from the battery unit suppliers, thus avoiding an unexpectedly costly transaction when exchanging near end-of-life battery units for new-battery units while making an informed decision to exchange the battery units by the consumer. The method enables securely recording the state information at the battery units so as to prevent unauthorized changes.    DETAILED DESCRIPTION - The state information is selected from a group consisting of usage information, environmental information, charge/discharge cycle count, information on charge/discharge current, information on charge/discharge voltage, information on charge/discharge power, information on charge/discharge time, information on energy reservoir charge capacity, information on energy reservoir charge stored, information on internal resistance of energy reservoir, information on acceleration experienced by battery unit, humidity information, temperature information and information on operation failures. The hardware/software configurations is selected from a group consisting of battery chemistry, initial charge capacity, end-of-life charge capacity, maximum allowed charge state, minimum allowed charge state, initial peak output power, end-of-life peak output power, environmental tolerances, device operating system version, device firmware version, device chipset version, manufacturing date, refurbishment/repair log and available sensors. An INDEPENDENT CLAIM is also included for a method for conducting a transaction.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a battery supply architecture.    Battery unit suppliers (3A, 3B)    Electric vehicles (4A, 4B)    Electric tanks (6A, 6B)    Storage/charging container (7)    Battery units (9)