Abstract: Peukert equation (PE) is used to compensate c-rates effect in state of charge (SOC) estimation. But the PE is inaccurate or inapplicable in many cases, such as batteries working under dynamic load. PE and its application are reviewed, its foundamental issues are discussed. In the PE, effect of remaining capacity and effect of coulombic loss are found to be confused, if PE is deduced from single stage constant discharge test. To avoid such confusion, a two stage discharge regime (Constant discharge-rest-constant discharge) is adopted, and then a new equation of C-rate versus the total discharged capacity of the two stages is deduced. The new equation (PE3) is also formally similar to original PE, except for a different Peukert coefficient. PE3 reveals the effect of C-rate on coulombic efficiency solely, so it is more applicable to SoC estimation in dynamic load circumstances. PE, PE3 are experimentally modeled and verified on lithium iron phosphate (LFP) battery.

Key words: Coulombic counting, Peukert equation, Remaining capacity, State of charge, Two stage discharge