We had had one experience of a near-miss on recovery of a recorder with lithium cells, from ~2,000 m water depth. We suspect that water ingress had caused gassing of the cells, and on almost reaching the surface the lid of the recorder literally exploded from the top of the housing. The force of the lid was somewhat limited by the recorder's steel inline frame. At the time i was preparing to attach a crane hook to the top of the frame, leaning over the side of a small boat. The open recorder housing flooded. We quarantined its remains for several days in a remote corner of the steel deck. Unfortunately, working in a remote region, we found we had no option for the disposal of the waste but to jettison the remains of the batteries over the abyssal plain - a very unpleasant experience.
After this incident we were extremely circumspect about opening the recorders (not SoundTraps btw) after recovery. Our initial risk assessment of the recovery operation had been to safely quarantine a recorder if there were any signs of damage or gassing. But i suspect these heavy, deep-water rated recorders may not show any such signs - we decided to treat each recorder subsequently recovered as 'potentially compromised'. We rigged a rope pulley system, which enabled us to remove the recorder lids in a direction away towards open deck and away from any personnel. The base plate of these recorders is also a removable part, with o-rings, and was also pointed safely away when opening the lid. Fortunately we haven't had a similar incident since, and the recorders have delivered good acoustic data.
It's also necessary to consider the risk of lithium batteries being caught in a fire onboard. In our case, we stored replacement and old cells in a dedicated area, clear of fire escape routes, etc.
For us, this was an important lesson learnt for working with recorders and lithium cells. In fact we try to avoid using lithiums when we can work with reduced recorder run-times, not only with regards safe handling, but also because of the problems of shipping and recycling lithium batteries.