Battery monitors and shunts to know how much energy is really left: Victron Energy SmartShunt 500A/50mV IP21 with Bluetooth, BMV-712 Smart with display and 500A shunt, modular Simarine PICO systems with shunt modules of 25A, 300A and 500A, temperature sensors and tank level modules.
On a lithium battery voltage tells you almost nothing: the discharge curve is flat, so between 90% and 20% of charge only a few hundred millivolts change. Only a shunt, counting amps in and out, gives real state of charge in Ah and percent.
The shunt is sized on the bank's maximum current and installed on the negative, downstream of all loads. Setup from the app or the display.
