Their M12 batteries don't have balancing (or a BMS inside), so they go out of balance and 'bad' very quickly. I've just added a balance plug to the outside of mine that I plug into my hobby Li-ion charger.
We have about 10 of the M12 batteries, about half are the 3 cell ones and half the 6 cell larger capacity ones. And every single one has gone completely out of balance within 2 years of use.
I plug them into a balancer and they last another solid 6 months or so.
The M12s have the pins too for voltage sensing in the charger (and tool maybe?), but they have 1 mega ohm resistors in line so cannot be used for balancing.