If you read my post,it's pretty straight forward what my problem is ,how much more info do you need?
You are new to the forum and may I welcome you here. We try to help, but we are often hamstrung becasue especially where a technical problem has arisen, we are unable to touch or measure the necessary elements to be able to accurately assess what's going on.
Some of us do have extensive professional knowledge and experience of caravans, and we have proven methods of checking many types of issues, but where as we have training and experience and the right tools to do it, not all users are so well placed.
From a professional perspective I know that often what may seem a simple issue to a user may be masking a deeper problem, and if we simply change the observed component it may well fail again becasue the underlying issue has not been resolved. So it is sometimes necessary to dig deeper to check what else may be going on.
When you think about a rechargeable battery that appear not to be working there are several possibilities as to why it appears not to be working for example ( and this is not an exhaustive list):-
The battery may not be connected.
Is it the correct type of battery?
Has it been wired up in the correct polarity
A fuse may have blown.
A terminal clamp(s) may be loose.
Corrosion may have cause the connection to become high resistance.
A connecting wire may have been damaged (physically cut, crushed or it may have been over loaded, and melted).
A switch may not have been turned on.
The battery has too much load connected.
The battery could be discharged.
The battery may have been left discharged for too long and is permanently damaged.
The battery may not have been charged for long enough
The battery might be damaged so it can't accept a charge.
A cell may have gone high resistance.
The battery may have lost its electrolyte in one or more cells
The charger may not be working
The charger may not be powerful enough for the capacity of the battery
The charger may not be turned on or the mains power circuit has tripped
Are the ancillary circuits telling the truth?
Not all the above necessarily have 'yes-no' answers, some may be dependant on other factors, and in your case obviously some would not apply.
So please don't get upset, we are trying to work out what your problem may be, and it will require some towing and frowing to get to the bottom of it.
If you are not prepared to work with us then you perhaps should consider using a mobile caravan engineer to investigate and correct the problem for you.