Most radios require two live feeds, one to maintain the memory which will be a constant feed whilst the second is a switched live feed, to actually power the unit up.
My suggestion would be that a previous owner has replaced the base vehicle switched feed for one from the leisure battery to ensure that they could listen to the radio without the ignition switched on, as it is normal for the radio to be disconnected after a few minutes of the ignition being switched off.
You'll need to research what has been done previously to rectify the situation or simply replace the feed for the units power from either the original source or pick up either a permanent or switched live feed from the fuse box.
That may sound difficult if you're not familiar with it , but it's not- any young fella who has put a fancy 'radio' into his car could do it for you in a few minutes. In my case that's my son's friend.
Thanks for all the feedback, another friend of mine has now wired the radio to a a live feed so he says, it works anyway.... but now the reverse camera is not appearing on the screen when put in reverse, seems to be one thing after another, any suggestions? It was all working perfectly before?
To me that suggests your friend has disturbed / disconnected the feed to the camera, there is of course the possibility that when the previous owner did or had done the electrical additions / modifications they weren't done very well.
Virtually impossible to diagnose your problems at a distance, your best bet if you are not sufficiently competent to diagnose and fault find yourself would be to engage someone who is.
I'm not trying to be obstructive but even 12 volts can and will cause serious fires when not handled properly.
An auto audio fitting person would probably take two minutes to diagnose it and another two to sort it - probably the best £20 or £30 he earns that day but that may well be your best option. I had my radio doing weird things - cutting in and out when it shouldn't, sometimes driving along and saying it was going to shut off in 60 minutes etc. My dealer sorted it during a routine hab service and didn't even charge! Probably a mistake on their part!