New leisure battery

Hi Gang, A friend of mine has a 2006 Dethleffs Advantage on a Ducato chassis with swivel seats and he is looking for a new leisure battery for it. He has tried Donaghey's and several other places but cannot find one that safely fits in under the seat, all the batteries he has tried are too tall and hit off the underside of the seat. He reckons that one 6" high would be ideal. Any suggestions as to where he might source a suitable battery? Thanks all.

Thought mine were about 6 inches as they are not that high, just went and measured them they are 9!!

Might be worthwhile checking out two 6 volt batteries, from memory I think they are a lot smaller.

But I thought they were six when they were nine

The other way around is worse