The ternary lithium battery has a nominal voltage of 3.7 volts and a maximum voltage of 4.2 volts.
Use 19 ternary lithium batteries connected in series to form a 72 volt battery. The rated voltage is 19*3.7=70.3V
Use 20 ternary lithium batteries connected in series. The nominal voltage of a 72 volt battery is 20*3.7=74 V.
It is therefore normal to display between 66 volts and 84 volts.