which battery to use first

Reading through the owners handbook for my sussex duo , well you have to do something on a naff day
It tells me that the sentry unit will switch over from the vehicle battery to the leisure battery if the voltage drops below 10.8 volts but that if the leisure battery drops in voltage it will shut down the internal systems and not switch over to the vehicle battery
So does this mean that I have to use the vehicle battery until it switches over ?
Cheers
Chris

The abilty to use the vehicle battery is intended as a backup facility if you inadvertently flatten the leisure battery. So use the leisure battery but if it runs down then switch to the vehicle battery to 'keep you going'. To ensure you can still start the vehicle, the appliances will switch back to the leisure battery when the vehicle battery indicates a voltage (under load) 0f 10.8v (of course as the leisure battery is flat they won't work!).

Incidentally, if on hook up you switch to vehicle battery , then it is charged instead of the leisure battery. This is very useful if you are pitched without moving for a couple of weeks and also to keep the battery topped up by charging a few hours every couple of weeks when the van is layed up.

Peter

Yes Peter is quite right.

You should never flatten a vehicle battery! The leisure battery, if it is kosher item, is designed for deep discharge but such treatment will kill a vehicle battery. So as Peter says this is very much a temporary backup solution, just to keep essentials like the water pump and toilet flush lump working for a few hours until you can hookup or run the van engine for a while.

I would strongly recommend anyone with a vehicle not used for long periods of time to work out a way to charge their vehicle battery. Remember that when you switch the ignition off there are still electrical systems working and consuming power, especially on more modern vans. Leave it for a few weeks and the vehicle battery will have lost a lot of charge and could suffer damage.