Modern Integrated charge controllers/AC inverter/and even some BMS equipped Li Ion batteries do that--And are even Internet connected (data, configuration, alarms).Another option is that some charge controllers (Midnite with their Wizbang Jr. remote battery current sense and possibly Outback with their "Flexnet" system).As you get more complex--There is more to configure, more functions, and possibly a bit more to debug if/when things go wrong.-Bill
Hall Effect Sensors are only good for gross measurements. So it could make the decision of Charging or Discharging. But you would still need a shunt ( a stable low value resistor that develops a precise voltage + or - ( charging/Discharge ) for the measuring system. Hall Effect Sensors drift quite a bit, daily !