Electric Bike battery management

The best approach may depend on your system requirements and how you want to structure your system. The bq76PL536 and bq77PL900 are really different products.  The bq76PL536 is intended to work in stacked systems and communicate with a host.  The host would typically make decisions on protection events, although the FAULT signal could be used to drive some circuitry. Cell voltage measurements are made in the device and available to the host.  The bq77PL900 can be a standalone protector, or can be used with a host.  It can directly control FETs within its range. It has internal voltage thresholds, but to read the voltage it uses an analog output which must be converted by external circuitry or the host. The internal thresholds do not match typical LIPO cell OV thresholds well, so the host would need to monitor voltages and make reasonable OV decisions.

A modular approach can be attractive in a system.  When building a modular system one thing to consider is the level shifting of communication paths.  This may be simple if you are sending a fault status down to a common switch circuit, or quite complex if you are sending cell voltages and control information. Certainly you must handle transients and voltages as the modules are inserted.  If each module has its own protection circuit, the module must be designed to handle the reverse voltage which could occur if the module which has a fault is not at the top or bottom.  If a standalone protector is desired for a modular approach, the bq77908 may be a good choice for a building block. A consideration with the modular approach is the complexity and losses in the current monitoring and switching in each module.

In general, the bq76PL536 would seem a good device for this system since it supports stacking to your cell count and supports a host.  Using a host allows some gauging or system decisions such as limiting operation to lights or communication to your motor controller to limit current when cell voltage is low. The bq76PL536 also has the -Q1 version if your system needs or may need this qualified part in the future.