The US Department of Energy Electric and Hybrid Vehicle Program activities include on-the-road evaluation of electric vehicles (EVs) by site operators at several locations throughout the US. Daily vehicle operation and maintenance logs and energy input data are recorded by these site operators, which provide useful operating information about the EV fleet of more than 500 vehicles. However, in evaluating improved products and components or in assessing the capabilities of vehicles equipped with different batteries, more detailed engineering data are required. To acquire the needed data and to better understand the differences in performance observed under field and laboratory conditions, an onboard instrumentation system is essential. Such a system is discussed.