Yes, Peter.
The reading should give you a pretty accurate charge state.
When 100% full, it should read about 41.5V.
Each 1 Volt drop is worth about 10% of the capacity, so
40.5V: 90% remaining
39.5V: 80% remaining
37.5V: 70% remaining
36.5V: 60% remaining
35.5V: 50% remaining
34.5V: 40%...