I'm a 2hr drive from the shop, so was looking for a fix. I found this
kaspars.net/blog/airbank-d13-pro-teardown and decided a reset might work, then contacted the Airbank Aus website. I got a quick and very helpful response from Pete who confirmed how to reset my unit:
Soft reset: press and hold the plus and minus buttons until RES appears on the screen.
that didn't work, EE4 error returned.
So next step was hard reset: just run it flat.
That worked and my unit is now fully charged