Two parameter estimation methods are presented for online determination of parameter values using a simple charge/discharge model of a Sony 18650 lithium ion battery. Loss of capacity and resistance increase are both included in the model. The first method is a hybrid combination of batch data reconciliation and moving-horizon parameter estimation. A discussion on the selection of tuning parameters for this method based on confidence intervals is included. The second method uses batch data reconciliation followed by application of discrete filtering of the resulting parameters. These methods are demonstrated using cycling data from an experimental cell with over 1600 charge-discharge cycles. (c) 2005 Elsevier B.V. All rights reserved.