If you operate the engine
in cold northern climates it's possible that the fuel
in the fuel tank
is summer fuel
which won't help.
company's put in additives during cold weather
for this reason, you also can buy cold start additives to put in the tank.
For all diesel
engines operating in sub zero temperatures add 30% of paraffin to the diesel(well mixed) and it will run quite happily. DO NOT add benzene/petrol.
If there's no preheat system I would buy myself a little gas blowtorch and taking the usual safety
precautions, remove the air cleaner and direct the jet of hot air into the air intake(taking care not to burn anything while someone turns the engine over to start, open the throttle fully before cranking and close to fast tickover immediately it fires on all cylinders.
I wouldn't recommend cranking the engine over for long periods for reasons already mentioned but also because the starter motor
will overheat and wear out prematurely.
You have also added another problem by emptying batteries which must then be recharged.
I hope this is helpful.