While changing battery cells in one of the unit Ram Cars. EE had removed a bad cell & picked it up by hand from on top of the battery. As EE was sitting down, EE tripped on a rock, causing EE to lose balance and fall. EE hyper-extended right elbow. EE worked to 8/26/16, then had surgery. EE came back to work on second shift, but started missing work on 8/30/16.