If you showed more of the schematic, it would help pin the identification down. There is a large number of BMS chips on the market. The ones I have seen have something like this at a minimum:
That is, at least one pin for a status indicator and one for setting the charge current and/or profile (e.g., PROG). Battery neg is also usually considered to be ground. Thus, in the absence of more information, the chip you show has 2 pins attached to ground (IN- , OUT-) and possibly a third one (B-). In other words, the pins labeled OUT+ would seem redundant to B+ as are the pins labeled OUT- and B-.
"B" can also be used to mean bias. That makes me wonder whether the chip could be some sort of amplifier (single) with IN+. IN-, OUT+, OUT- and bias.