Jump-starting high-amperage diesel engine with a car with a smaller battery

No, you need the full amperage power to crank the diesel at sufficient speed to start . It is unlikely to start if cranking at low RPM ; A gasoline engine is more flexible in this respect. Most have heard a gasoline engine barely turning over but then the cylinders start firing and help the crank speed . A diesel generally won't do that. I though of getting a diesel for a cold climate and asked an automotive engineer about pros and cons; he said starting a diesel in cold weather is basically a battery test. If the proper battery is in good condition it will start, a weak battery will not start it.

I have successfully jump started my diesel Transit (with a great big lump of a 2.4 litre engine) from a small car, more than once. Things that help are: warm ambient conditions (so you can start without preheating using the glowplugs); and revving the helper car well above idle (but no need to redline it) for a good few seconds before trying to start. If you were trying to charge the battery using a small car idling, you won't have charged it much, similarly if you used a mains battery charger.

Keeping the battery topped up is a better idea. My approach is a 20W solar panel on the dashboard, with a charging regulator that automatically switches to trickle charging. This save messing about with mains cables (and I had the panel for topping up the secondary battery - it's a campervan).

In the particular case of this car, I had a tow truck come and jump it. Not only did he have to use a 1000 amp charger, he had to augment it with his truck battery. I drove the car for 50 miles or so, turned off the engine, and again it wouldn't start. So, bad battery. I had it replaced and no more problems. Thank you all for your input.