Ace Siena control panel/solar panel/leisure batter

Hi, I'm new to the world of MoHos and have an Ace Siena.  It developed a fault whereby the control panel would not turn on and the steps would not deploy.  Back to the supplier under waranty and they "fixed" the problem by resetting the control panel.  They weren't terribly forthcoming about why it would need that but hey-ho.  

Now and week or so later and the control panel is a little flaky in that it won't always turn on but when it does, the leisure battery shows about 10 volts and the LEDs on the charger relay show the solar panel 'knows' that there is an engine battery but is dead as far as the leisure battery is concerned.  Start the engine and life returns to normal, both batteries charging and will charge all day on the solar panel.  Overnight the leisure battery dies and we go through the same routine again.

I am assuming that this means the leisure battery is effectively dead but before I replace it, does anyone know if there is another possible cause for these symptoms?

Thanks.