Battery voltage is pretty good but only after it’s settled a bit.
Here is a good estimate and just multiply the voltage by 6 to get your total battery pack voltage.
And maybe measure each battery every 4 months to be sure they are all staying balanced(close to each other in voltage).
You don’t want to go below 12.0V( 72.0V ttl ) after it has rested for a few minutes. If while driving you see it go under 72.0V it would be ok but that should also be an indication you’re very low on charge and likely should only be a mile or so from home/charging.
I have used this one before, it fact I have one in my current 2016.
It works, I have not measured the accuracy but it does have some nice features like being able to set the high and low battery values (like 99v and 75v) so the percentage left before empty is accurate.