Just today we had to move a Deutz D40.2 (1962 or so) out of the way and the battery (something like 12V 130Ah or so) wasn't up to it. So I first tried helping out with a just-charged car battery (12V 36Ah, used for electric fences), then with a running car (old Mercedes). I finally unconnected the tractor starter battery (which probably had just gobbled up most of the previous attempts) completely and just used the running car (with someone pressing on the accelerator) and basically gave up when one of the starter cable clamps' metal started glowing and melting through its plastic.
The starter motor of the tractor was at best moderately impressed, with an action that would have corresponded to a mostly empty starter battery of the tractor.
So what's the actual starter current like here? I know that with a fully charged starter battery, you'll have not all that more than a few minutes of actual starting before things get ugly. The pre-glow current is something like 3x10A and I think one is better off doing this a minute too long rather than having two bad 3 second starting attempts.
I don't have a current measuring clamp myself and certainly no current meter that I could viably put in the middle. I think I measured the voltage during start at some point of time, and it dropped something like 2V or so while starting.
Are there any hard numbers regarding the starting current? Because this feels a bit excessive to me. It does start as long as the battery is in reasonable state.