Hello, What is a PDU convertor ?
Leisure batteries are normally charged through a split relay by the alternator.
I use a cheap voltmeter plugged into an accessory 'cigarette' socket wired to the leisure battery to, crudely, monitor the charge.
OK, I looked up PDU; facilitates 'all' the leisure electrics.
Seems to provide charging to the leisure battery from the mains hook up.
As far as I am aware, my mains set up does not use a PDU, just a split charger and fuse/rcd.
So, I do not think my leisure battery is charged when connected to the mains.
That Varta battery seems to be for starting small marine craft !
Imho, starter batteries are not suitable for leisure batteries.
I stand to be corrected.
Have you measured the leisure battery voltage ?
Off load, and on load ?