According to some battery whizz, a leisure battery needs to stand for 4 hours before you measure the voltage to see exactly what state of charge it is.
So any gauges are at best an estimate if you take readings before that. Considering that there is very little voltage difference between a fully charged leisure battery 12.7v or over to half charged at 12.4v, reading a battery too early will give you a false reading. Especially is this so with a split charge relay connected where the van's alternator can be kicking in a voltage on 14.4v.