Passive cell balancing

Abstract

Battery systems and procedures for balancing batteries are provided.A battery system comprises groups connected in series, each group having an equalization window defined between an upper voltage V1 and a lower voltage V2; each group having a minimum open-circuit voltage V3; V1 > V2 > V3; each group comprising at least one cell; and each cell independently having a self-discharge current less than or equal to a self-discharge current ISD; and a diode arrangement configured to passively reduce a voltage difference between groups, wherein: the diode arrangement comprises diodes; each diode is electrically connected in parallel with a respective group; each diode is configured to discharge the respective group with an equal first diode current ID1 at voltage V1, with an equal second diode current ID2 at voltage V2, and with an equal third diode current ID3 at voltage V3; ID1 > ID2 > ID3 > 0; and ID1 > ID2 + ISD.