Hi Paul
I personally would not buy electrical items from ebay, but saying that I expect hundreds of people have bought good stuff from reputable suppliers.
You can check out you local stores ie. halfords, motor mart type stores, but better still a caravan supplier.
An intelligent charger does a few things, first it will charge your battery up to a set voltage, then it will switch to what is called a pulse charge to take the battery to its full charge,
once it has reached its full charge, the charger will then switch its self off, if it is left connected to the battery say over the week-end, it will then switch its self back on to keep the battery charged to its full capacity, and will keep doing this until the battery is needed.
so in affect you can leave the battery conected to your charger without any danger of over charging it.
The one you pointed out on ebay looks like an ordinary charger and discriptions on ebay can be a bit vague at times.
if you follow the above and when buying one, read the specifications on the box or item its self. if it does not give you the above spec then its not an intelligent charger.
make a new post and ask the guy's on here, who have bought an intelligent charger were the best place and price is, and make your choice from that as there are so many to choose from.
I hope this helps you a little??
Regards