Why you shouldn't buy cheap imitation Makita Li+ battery packs[1].
(With a supplemental lesson on the foibles[2] of the official ones. PSA: If you haven't used yours recently, go and charge them!)
[1] The combination of a complete lack of cell balancing, combined with a tap off the first cell to power the battery electronics means they're doomed by design, no matter how good the cells themselves might be.
[2] Short version: They also power the electronics from the first cell. Which can drain it flat if left unused for too long.
When you then attempt to charge, it refuses. If it fails to charge charge three times in a row the electronics deliberately brick themselves[3] via a fusible link. Bastards.
[3] So if your Makita battery pack fails to charge, don't try again: Get someone with electronics-fu to take it apart and persuade the first cell back to life first.