Autotrail battery problem

Hi - can anyone help please - I'm tearing my hair out! I have a 5 year old Autotrail Cheyenne 660SE. Since purchase a year ago we've had nothing but problems with the batteries not holding a charge. We had it serviced a few weeks ago and have taken it away since, but when we plugged it into the mains yesterday the alarm came on (and couldn't be switched off) and it seems both batteries are completely flat. Neither will take a charge and there's no display on the control panel. 

The engine battery was new in Oct, the leisure batteries are likely to be the originals. Any ideas? Also, does anyone know of a mobile battery service in the Cardiff area that also deal with leisure batteries?

we love caravaning, but this is getting us down :(