It's in my AC Cobra. The battery is in the trunk. Thats why the batt is grounded to the chassis and the chassis is grounded to the trans. Also has a starter Solenoid on the firewall.
Since different configuration than the standard, more connections, longer cables, and maybe too small of wire gauge.
First, with engine running, measure voltage at BATT stud and alt case.
Then measure across battery posts.
The difference is the power lost due to the three items mentioned.
The longer the wire/cable, and smaller gauge, the more power lost through the conductor.
High current through a conductor heats up the conductor, and resistance goes up, less power at the other end.
All connections are the same. Add up the 0.1 volt across the connections, and same principle, more resistance, more power lost.
The same applies to the return/negative side.
Think of a 100 foot garden hose. Nozzle off, lots of pressure.
Turn nozzle on, and pressure differential between the faucet and nozzle, loss contributed by the water flowing through the hose - the resistance of the hose.
So what is one to do? Granted, with the auto selected, it is a race car in sheep's clothing.
Hence, the designers/engineers used the bare minimum requirements because of weight reduction.
As long as the engine starts one time for the race, the requirement is met.
One fix is running either #4 or #6 AWG cables from alt case and BATT stud to the battery posts. Solder the terminals to the cables.
Another is run the next bigger wire/cable gauge for each wire installed and solder the terminals.
On battery cables and jumper from solenoid to starter, and return cable, use multi-stranded cable, ie, welding cable, 2/0 AWG, and copper terminals.
Run a single ground cable from engine block to battery.
Wire brush those connections.
I forgot, you can measure the cable loss from one end of the cable to the other. On the DMM lead, chose one, doesn't matter, add the selected length of wire extension to the one lead. Turn meter on, select the voltage range, and touch the lead extension and other lead together (include the wire extension) and let the meter self-zero. When zero appears, meter is ready for a more correct reading of loss of the same cable from Point A to Point B.
Turn starter on and read the loss.
By getting a bigger battery, the cabling is the weakest link - bigger battery is more current available, but still only X amount of current can travel through the wre/cabling.
Think of filling a 5000 gal tank with a 3/4 inch garden hose and a 2 inch fire hose - which one will fill the tank the fastest?
If you get paid by the hour, use the 3/4 inch hose.