None of these systems can be made modular past this committed decision point.
Daft question, WHY NOT ?
AIUI the charger/monitor is a self-contained unit in a box....it interfaces with the aircraft systems and with the battery it controls
The battery, IMHO should ONLY interface the control box(charger-monitor) It's a bit of a stretch to say that this is met by the contactor/relay within the battery, being switched by the controller. However
The battery and controller together form (or should) an integrated, self-contained electricity storage and supply system.
Physical space should be the only problem,if the storage-device (battery) and it's associated controller are designed to be compatible to each other and the power-requirements (aircraft) they are hooked into.
What am I missing?