Two Ultra-Thin Loop Heat Pipe (ULHP) prototypes with parallelogram and trapezoid evaporator configurations were developed for battery thermal management system (BTMS). The dissimilarities between their heat transfer characteristics including the critical work angles, the start-up features, the thermal resistances and the flow instability were all explored and compared with experiments conducted under multi-orientations. The specific influences of these two evaporator configurations on the stable operation of ULHP have been fully acknowledged. The experiments results demonstrated that both the two ULHP prototypes displayed good performances with limited assistance from the gravity, meeting the demand of working under multiple orientations. Specially, the parallelogram configuration showed superior performance in resisting gravity by better suppressing the flow instability, the ULHP could not only start up under 15 degrees inclination, but also the recession in heat transfer capability with placed angles was limited in 4%. Meanwhile, a reasonable mathematics model was established based on the steady operation state of ULHP, the predicted value fitted well with the experimental results. (C) 2016 Elsevier Ltd. All rights reserved.