Removing Back on Voyage - Now 6 years old

I’m attempting to remove the back on my Voyage in order to replace the battery. The videos from iFixit and others toss off removing the back as just sliding it down. That isn’t working on my now venerable Voyage (they were made when it was new). I’ve tried unsealing the side seam by running an iFixit triangular plastic shim, but am not having much luck. Does anyone have any suggestions on how to get the back off without busting the device. I assume the age is the problem with the seams welding shut.