The tool battery also needs balancing.

Due to the nature of charging tool batteries, it is natural and common for cell balancing to change depending on the high load. But a genuine charger doesn't hold it perfectly. Therefore, it is common for batteries with cell balancing to no longer charge. If you do cell balancing , you can use it well for a while.
Moreover, if you create a jack for balancing, you can balance without disassembling the battery. Of course, you need a charger or balancer that balances battery. It's a DIY that's worth trying to take care of your batteries.