Most decent battery management systems out there employ balancing, overdischarge protection, overcharge protection, etc.
Almost universally they state that the charging voltage is just 4.2*N_cells. This is fine, but it is clearly a lower limit voltage for charging to happen. How high can I provide?
Do I need to build a buck converter to provide exactly that voltage, or can I just rectify 220V mains and push that in, and the BMS will limit current accordingly?
How about the case of regenerative braking in EV systems? If I rectify the output from motors, that voltage will surely go over the 4.2*N_cells figure. Is that ok?