I have taken apart two packs which belonged to an SR-90.
There may be some good cells hiding behind the protection circuit.
In these packs there are six 18650 cells in total, in two separate banks, 2S3P arrangement. In each of my packs, one of the banks was <2.0V, and cells this low should not be recharged, so they got sent to recycle. The other bank was >2.0V and I kept those cells. From the two packs I got six total good cells. I use them for benchtop projects and such, but I could have rebuilt one of the packs with those.
To restore the pack you should disassemble it. You can use large snap ring / retaining ring pliers such as Channellock model 927 or equivalent, or use an adjustable retaining ring spanner, to unscrew the retaining rings. There is some tacky thread locking compound but a robust tool will succeed in removing the retaining ring. Then you will find the protection circuit board and the six cells, enclosed in shrink wrap. Cut the shrink wrap to expose the cell banks.
Each bank of three cells is spot welded together onto nickel sheets. The connections to the protection PCB / BMS are made with copper wires. The copper wires are soldered to tabs which extend from the nickel sheets, and the other ends are soldered to the PCB.
Maybe you will find that both banks are >2.0V and you are keen to recharge them manually. Maybe one or both are not revivable. If they are out of balance it may be advisable to charge each bank individually.
You have some options depending on what you discover. If you wish to rebuild the pack with new cells, you will have to acquire a 2s3p pack with the same configuration, shrink wrapped and ready for deployment, or use loose cells, and determine how you want to establish the connections. It could be done via a pack welder and nickel strips, or it could be done without welds via contact plates. There should be enough room in the pack for a custom solution like that, if thin copperclad PCBs are used. I would ditch the stock BMS solution (protection pcb) because it clearly has a problem with cell balancing and parasitic drain. This will provide even more room in the tube for contact boards and such. The stock charging solution might not be suitable for charging the new configuration without the original BMS in place, depending on the voltage it provides. If it provides 8.4V it should be ok. If >8.4V, manual charging via a hobby charger may be the way to go. Using a hobby charger (or an adjustable power supply) I’d charge a 2s pack to 8.2V rather than 8.4V, to avoid possible over charging.