Leisure battery?

It shows that it is about 70% charged.

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Many thanks you two. That's reassuring, however, although it translates to about 70% charged I wonder what this tells me about its actual condition. Now please appreciate I know little about such things but I recently heard about the use the of a ¿drop test.? which is used to establish the true condition of a battery. What is this and how is it performed? Again, any help towards my understanding would be appreciated.

As mere mortals we only have voltage as an indication of battery health. It is possible to use a bit of kit that places a high drain on the battery and then measures its CCA (current delivery) profile, this is the only way to determine the true state of battery health. It is possible with new modern digital electronic battery testers to do a simulation of this. These type of kit are service tools and not available to casual users. 

If you are concerned then charge the battery, measure the battery voltage, run as much 12v kit as you can in the van for 10 min. Turn everything off and leave it for 20 min. Measure the voltage again. If it stays above 12.5 then generally you have good one assuming you start fully charged at about 12.8v. 

Other than this then you will need to run it to a service centre and get them to do CCA and capacity test but you really don't have anything to worry about, batteries tend to be good or bad.

fully charge the battery and then take it to a local auto spares shop, they should have a drop tester, (it looks like 2 prong with a thick spring in between and a dial meter). they probably won't charge you as only takes 20 secs.

https://www.ebay.co.uk/itm/Sealey-Bt91-3-Battery-Drop-Tester

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My concern was that I realIy expected the battery to be shot. Guess on this occasion I was being pessimistic. This was compounded by the Storage Owner who dampened my original surprise with a sharp intake of breath and that caveat about just using the initial reading.

I'll do as DD suggests in the first instance, see as it goes and hope for the best for daughter or possibly dad's pocket.

Thanks again to all.

It sounds fine. Recharge with a smart charger and try and top up more often. Don’t drop test it.

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Without knowing the battery's identity and also with that access to the makers "State of Charge vs non load Voltage" tables,  it is guesswork on quoting how charged it is.

However it is evidently not in a "good" condition to be left that low. For the best chance of success recharge ASAP with a charger having a "desulfation" phase, such as most CTEKs.

With the trend nowadays to be using traces of cadmium in the lead alloying on most batteries we are likely to be buying, they have a bit higher voltage  throughout the range of SoC than typically the case some years back. Therefore I suggest at 12.39 the battery will be unlikely to be much above 50% charged. As said earlier this is not healthy and will be inevitably ageing the battery quite significantly.

How useful the battery will be for your daughter depends also on what use she asks of it, if she is only an EHU user with modest mover requirements then probably its loss of ability to hold a big charge will go unnoticed. Where it will have ramifications is if her use is extended off EHU camping where retention of capacity is all important.