Originally Posted by
steveG
Looks like it was due to faulty batteries.
I knew the second battery was suspect, but after charging overnight it was still no good so I declared it dead.
Supercheap do free battery tests so I drove into there and had the cranking battery tested. It dropped to 9v during the half a second it took to start.
End result is that I've removed the second battery and chucked it, put the original cranking battery in its place, and installed a brand new main one from Battery World.
I know the current second battery isn't great, but it will do what I want for now.
All seems to be happy now, but I still need to test that its OK after draining down to the cutoff voltage.
Steve