Minimum voltage to start a diesel

Derek,
You have some good graphs up your sleeve!
Yeah, I expected 12.15 to be less than 40%, but obviously not. The preheat element in mine pulls 80amps, so it says a lot that a battery can still easily crank the motor.

Axle,
I have two batteries under the bonnet - joined by a switch. 99% of the time I leave them paralleled. I like to run identical batteries, and leave them paralleled so that the batteries don't do much work and last longer. Also handy if I were to winch. And I tend to go driving every day.

So the fridge drained two Exide extreme batteries - both to 12.15V. According to Derek's diagram, I drained off 60% of their capacity (160Ah) - So the fridge may have used up to 96Ah over 5 days - the fridge was an empty 40l Engel with the lid off.

I thought it was interesting because Toyota provide twin starting batteries for the 100series with the same motor, so it can start in the cold. I reckon there must me a lot of overkill in their thinking.

cheers
phil

Remember too that with the two batteries in parallel you can get the current out much quicker than a single battery of the same size.
You also probably have the truck in a garage or shed so it would be much warmer than a winters morning outback.
I've noticed with the Humvee which is 24v and has two N50zz's (next size down from the 70's which unfortunately won't fit in the carrier) that it will start the engine after 4 days of running the frig and camp lights, but it wasn't very cold (easter). I don't have aux batts and the frig is 24v so current draw is around 1.5 amp.

I forgot to add that most diesels require a minimum cranking speed to fire so this is more cricitcal in some cases than others.
The Toyota's are pretty good in this respect as if you can warm the glowplugs a little and get the engine to turn over they will fire, the 6.2 in the Humvee needs at least half of the glowplugs and needs to spin over pretty quickly to get it going. The advantage is the 24v, half the current drain compared to 12v.