Follow these instructions to obtain PDF diagrams for your unit so you can figure out what's wrong. Incidentally I think the batteries (2 X AA) just light the cassette full warning light but your unit has a 12v supply for the flush, hence the E at the end of your model code.
Thetford Spares and PDF’s from Website
Follow the information for access to Thetford website and free repair pdf downloads.
Uk & Europe: www.thetford-europe.com
Home page. Select English
Select customer service (top line)
Select products from top line
Select built in or portable which ever applies.
Select user information from list on right.
Select repair instructions from list on right
Select built in or portable which ever applies.
Select your toilet series model number from right list.
You will now be in the PDF listings for your range of toilets just select those that apply to your toilet and down load them they're free.
As you go through watch for 'ask Thetford' on left listings
you may not find what you want and you can send them a message.
For safety reasons Thetford do not offer repair advice for fridges. Refer to service centre
CC Member 18017873
July 2012
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix toilets.