Multiwall carbon nanotubes (MWCNT) with a diameter of 30-50 nm was added to the negative electrode of a Ni-MH battery in order to study the effect of its purification treatment on the electrochemical performance. Three different reflux assisted digestion methods were analyzed. MWCNT were structural characterized before and after purifications by means of different techniques such as HRTEM, EDS, SEM, XRD and FTIR. Subsequently they were incorporated into the working electrode to evaluate the electrochemical performance by charge/discharge cycling and rate capability. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.