Ordered a new Sterling Power battery monitor, this one has built in MPPS controller for the solar panel and also looks after the stop start/ regenerative braking system. The old one does the job but not quite, more suited to the pre T6 fancy electrics.
Also fitted a new main battery 85 amp suitable for the van but old OEM was only 65 amp. Bit of a squeeze but got there.
On that note:
To be able to change the battery yourself you need to keep the 12v electrics working whilst you change over. A search in YouTube found the way, quite simple really! A pair of jump leads and a slave battery!
Connect jump leads to the main battery terminals and the corresponding slave battery before removing the main clamps from the battery, be careful to isolate live terminal I used a rag. Remove old, insert new, hook it up then disconnect the jump leads. Job done no loss of info and all instruments/ radio/ windows all working perfectly.