I have moved my posts to the thread already created about the use of a multimeter.
I really dislike doing any form of electrical work as my lack of understanding in electrics invariable leaves me frustrated.
However I decided to check all the connections of the battery and the connections and fuse for my battery tender.
I think I have isolated the problem, the fuse to the tender was slightly rusty. It was not blown as confirmed with the multimeter. So I lightly sanded the crap off. It's back in place and hey presto. Battery holding a charge and now charging.
Thanks for the excellent help and advice.