EC480 battery voltage

The vehicle battery voltage is showing around 4.5 volts on the EC480 however the engine seems to be starting OK. 
The voltage shows very low even after a good run to charge it up. 
Could this be a fault with the EC480?
The leisure battery volts read OK. 
Any advice would be welcome. 
Paul

You need to put a meter on the battery to begin with. They are under a tenner and an essential in the van toolkit for me.

Good advice. I usually keep a multimeter in the van but we came away in a rush and forgot to put it in. I will buy a cheap one on our travels.

I’ve got a couple of these, nice and simple and there is a Screwfix everywhere!

https://www.screwfix.com/p/lap-ac-dc-digital-multimeter-600v/75337

We passed. Screwfix this morning so bought the multimeter at under £10!
The battery is reading around 12v at the cigar lighter socket but will check the battery terminals tonight. 
I am beginning to think the problem is the battery reading sensor. Luckily our van is still under warranty so Marquis can have a look on our return.  
Thanks for the advice.

12 volt at cig lighter 4.5 volts at the controle display , must be display fault .

I agree. The van has to go back to Marquis sometime soon so will get them to have a look as under warranty.