Adding a bit to this old thread, I just purchased a dead R89 repop battery and had great success in just popping the top off of it to replace the AGM Odyssey PC925 battery. The tops are glued on but glue really does not stick too well to the polypropylene plastic. I used a 3 inch putty knife and worked around the overlap edge flexing the top cover outward slightly. I could hear the glues fracture here and there. Bits and pieces of the glue would flake out once in awhile. After working all the way around a few times it was still stuck. I then through caution to the wind a bit and inserted the putty knife at the corner and with a firm upward hit the corner popped loose. I then moved to the other corners and did the same. More success. Then I worked from there along the long sides and it quickly popped the top off all the way. Then i tried to pull the battery out and discovered the battery was glued into the bottom of the case. There is about a 1/2 inch gap from the top of the internal battery to the top edge of the battery case. I then flipped the battery upside down and dropped it from about a foot up onto the garage floor. 3 or 4 times of this with pushing it down faster and the battery broke free of the outer case.
Also, I am leaning towards this battery as a replacement:
https://www.amazon.com/dp/B095T18XKP...v_ov_lig_dp_it
Always had pretty good luck with Interstate batteries.
Hope this adds a bit to this helpful thread.