In　hybrid　electric　vehicles,　one　of　the　key　tasks　for　the　battery　management　system　is　to　maintain　the　batteries　in　the　proper　range　which　can　fulfill　the　requirement　of　energy　flow.　Considering　the　dynamic　operating　conditions　of　traction　batteries,　an　equivalent　circuit　model　is　proposed　to　simulate　electro-chemical　characteristics　of　the　battery.　According　to　the　dynamic　equations　of　the　circuit　model,　internal　parameters　can　be　induced　through　battery　response　under　pulse　current　test.　Different　experiments　are　implemented　exploring　how　the　internal　parameters　vary　with　the　depth　of　discharge,　which　is　critical　for　the　battery　management　to　determine　the　energy　conversion　range.