7.8 Energy efficiency7.8.1 Purpose The purpose of the energy efficiency test is to determine the battery system round-trip efficiency by calculation from a charge balanced pulse profile. For high-power battery system, the energy efficiency of the used battery system has a significant influence on the overall vehicle efficiency. It directly affects the fuel consumption and emission levels of a vehicle equipped with a high-power battery system. This test applies to high-power battery systems only. 7.8.2 Test description The test simulates the following driving situation: for acceleration, for example on to a highway or during the overtaking process, the vehicle driver requests the maximum vehicle power (max. battery discharge power). Following that, there is a cruising phase without battery performance for an assumed time of 40 s. After that, there is a regenerative braking period assumed for 10 s to recharge the battery. Of course, the actual demands are different because the drive systems of the vehicle suppliers differ, but for reasons of comparison and evaluation of battery pack and system, it is a common base. 7.8.3 Test procedure The following conditions apply: — RT, 40 °C, 0 °C; — three different SOC: 65 %, 50 %, 35 %; — 30 min rest period before each power pulse sequence application for equilibrium; — adequate rest period (see general conditions in 5.1) after temperature change for thermal equilibration;— current profile for energy efficiency characterization as described in Table 23. Table 23 — Energy efficiency test profile Time increment s Time cumulative s Current A0