Battery charging

It looks like your battery is kaput, as you describe. The fact that it returns to 13V when on EHU is thanks to your charger.

1) The panel should look after your battery, so long as there’s nothing drawing more power out than the panel can put back in. An alarm system might draw significant power as would anything left on standby or unintentionally (like a light). Try to place the panel so that it’s is not shaded by tress or buildings.

2) It should not matter to leave your van connected if your charger is a ‘smart’ variety. ‘Dumb’ chargers will dry your battery out and cause premature failure. If you use the van monthly, that should keep the battery topped up nicely. Leave it on EHU for a day after your return, if you have a motor mover or did not have EHU while away, to bring the battery back to full charge.

3) If you turn the master switch off, you will get no benefit from EHU. It will need to be on.

4) I’d expect your van to have a charger on board. It ought to be good enough to do what you need.

The battery at 8.5 volts is certainly "flat" by any standard though not necessarily "kaput", however being so low and if being there for long will kill it.

As said leave it on charge for 24 >48 hours and see after that how it holds up. Even if that seems okay the real test is putting it to "work" and seeing how long it can hold up for.

There is a high probability that the battery is no good as draining them too low and not promptly recharging is a typical abuse they get in caravans.

A 70 Watt panel if kept clean and "seeing" the sun without too frequent shadows should keep a battery healthy. Grime and shadows massively reduce solar panel performance.

"...Try to place the panel so that it’s is not shaded by tress or buildings."

Always pays to keep your hair tidy. 

Always pays to listen to the voice of experience! 

Is your caravan against the house wall? does the sun reach there? It might be producing less than the van is using.

No its not against a wall, no alarlm fitted to van to consume power either. Have taken the battery out & we are attemting to charge it as we speak. We are away this weekend if the battery will get us up the drive lol

Good advice above. Some vans have dual chargers like the Sargent system which will boost charge a battery then bypass it once fully charged so that it doesn't continually have current forced into it, however, most vans have a conventional charger which will give a regulated output but should not be permanently connected. Therefore, if you have been using the van off of EHU then as soon as you get home you should disconnect it and recharge with a conventional charger. The van charger will only supply about 13.8 volts approximately which is not enough to properly recharge the battery and you will get significantly reduced life. 

Battery chargers fitted in caravans are not powerful enough to charge a flat battery. If you have taken it out then hopefully you are using a more powerful charger. If you need the battery to get you up and off the drive then it sounds as if you are using a motor mover and you will be depleteing the battery even before you go away. At this time of year a solar panel will probably be limited in doing it's job. Ah, hitchglitch posted whilst I was writing

Battery chargers fitted in caravans are not powerful enough to charge a flat battery. If you have taken it out then hopefully you are using a more powerful charger. If you need the battery to get you up and off the drive then it sounds as if you are using a motor mover and you will be depleteing the battery even before you go away. At this time of year a solar panel will probably be limited in doing it's job. Ah, hitchglitch posted whilst I was writing

Its not so much the lack of power, they produce enough current but a battery needs a 14.4 volt regulated charge whereas the van has to supply a steady load for the 12 volt system. Usually the compromise voltage is about 13.6 to 13.8 volts which is not enough to properly recharge a discharged battery but enough to keep it topped up without blowing up anything in your 12 volt van system.

Ok, thanks for all your help so far, much appreciated. What voltage should a fully charged battery read? We have had it on charge now for 24 hrs & it's reading 13.2v. We've borrowed for now a C tek charger (mxs 3600) & it's showing fully charged with this unit, also checked it with a Ring multi stage auto charger & showing fully charged with this too. There is a battery condition window on top of the battery that should be Green if charged, this is Black which means it wants charging. Completley confused now......