Harmony 2001 Leisure battery

Hello everyone! We have recently acquired our 2001 Harmony; it is proving a less than 'harmonious' at the moment as we can't seem to get the leisure battery to work/hold charge. We are complete newbies to this and are trying to work out how to get to battery so we can check the charge and the fuses. I cannot fathom how you can access it (or remove it, if we need a new one)??! I can see it, touch it, but I can't get my hands round it! Any suggestions please, as at the moment we can only run things on hook-up through the leisure battery with the battery charger button on. I understand this is not good for the battery!
Anyway, an idiot's guide to getting to the leisure battery would be much appreciated!
Thanks!

If under the seat , the seat has to be removed

Oh rats!!

I can recommend that if/when you come to do the work, be prepared, and have someone else available to help with the lift.

In terms of outright weight they are typically not overwhelmingly heavy, but the combination of weight and the need to lean into the van to lift are not great for your back if yours is at all sensitive!

Thank you, Roopert I will definitely bear that in mind!