Hi Odogster,
coincidentally, I now have the same problem with my Enertia+.
Error V58 means that the 12V voltage is out of tolerance. The fault is most likely a faulty DC converter Sevcon 80 / 12V or poor contact on this converter.
Try to remove the bottom cover and after turning the key to the ON position, measure the output voltage on the DC converter (two thinner wires).
Also try to clean the DC converter connector and check if it is not too loose in the connected state.
Cheers
Karel