this is a J with the 4 d battery pack? and then you added the 3358?
6 rayovac D's in any battery accessory typically give 90-120 days before switching to internals or the second bank or dying in the case of the 6d replacement pack..
differences in total day performance would be if the Camera in question is used as a link, has a high volume of images , or a very low signal.
if none of the above, i would swap battery packs to determine if its the 3358 or the camera, make sure firmware if up to date if its old in the J with the 3358.
If you can determine its the camera or the 3358 is the issue you can call cs and set up a return.