Earthing probs - advice sort

[Fargo]

Righ, had the clicky click of a dead starter motor the other week, finally got round to fitting a refurb kit and it started first time.
Couple of runs later i get the same prob, however it jumps ok only when jump lead is on engine block.

Ive got 12v on both batteries.
ive got 12v between batt + and starter motor housing.
Ive got 7v between batt + and starter motor housing when trying to start.
ive got mV between batt - and starter motor housing and also when starting.

what to do

Help help help.

[NiftyNev]

Test the batteries during cranking. If they drop to below 10 Volts then there's your problem.

Nev

[Fargo]

finished charging both batteries, 10.3/5v on crank, 12-13.5v on 2k rpm.

lets see what happens now..

[Apache]

In theory you should have 14.4v at a healthy battery when the alternator is charging. Lead acid's s should be charged at 2.4v per cell you see.