VDM

Voltage Display Module.
As the name suggests, it displays the open circuit voltage of the battery, an additional feature is that it tells the number of days, this is helpful with FIFO at the factory/distributor end and with warranty giving the number of days since installation. VDM is designed to be very efficient barely consuming any current while it works, so that it does not affect the host battery. VDM is small and modular, making it convenient to attach to host of batteries.