Cable length is slightly under .3 metres total round trip. This gives 0.21 volts drop at 130 amps using Ancor's published resistance of the cable. Also, Lofrans reckons #2 wire is OK for up to 25 metres round trip

Agree the drop is large. I will dig into the battery and measure voltage at its terminals and check the other things mentioned

Since my first post, we measured current drawn at no-load, with chain off gypsy. It was 180-200 amps, with windlass turning at 40 rpm, which corresponds well with the advertised maximum line speed of 40 m/minute

The main shaft turns freely by hand with the chain off the gypsy.

I am amazed at the high current drawn at no-load. Anyone got ideas?