We report here the characterization of Li battery electrolytes based upon the N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl) imide ionic liquid (PY14FSI) with lithium bis (fluorosulfonyl) imide (LiFSI) as a support salt. These electrolytes show low viscosity relative to other pyrrolidinium-based ionic liquids (ILs) and corresponding higher conductivity at subambient temperatures. The melting point of the IL decreases with the addition of LiFSI and concentrated samples remain totally amorphous. The electrolytes exhibit decreased thermal stability and increased parasitic cathodic reactions with increasing LiFSI fraction relative to the pure IL, probably due to a higher impurity level for the commercial LiFSI. Despite this, the electrolytes have excellent lithium cycling behavior at 20 degrees C. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3208048] All rights reserved.