Is there a correct battery voltage chart?

Voltage is a horribly inaccurate way of measuring battery capacity. That's why the charts are all over the place. Battery design, specific gravity, temperature, charging or discharging currents, and probably some other things come into play.
To really know what's in a battery you need a battery gauge. A battery gauge will have a shunt; if it has no shunt it's not a battery gauge. Tri-Meteric makes a nice one as do Victron, Magnum, and Outback.