More infos, that video guy linked
U.S. Coast guard maintenance procedure card RESCUE AND ASSISTANCE RSS583042.0 REV’D: 08/22/12
RSS583042.0_PLBAUG2012.pdf
another copy MPC_PEPIRB.pdf

It shows how to reinstall battery packs and perform the self-test smile

Other guys that did these things
DIY ACR EPIRB Battery replacement
749245ACR ResQLink PLB Dissassembly- AKA the $10 battery replacement. | Adventure Rider