The booster button is not a toggle switch. It must be held down to help charge the starter-battery. Keep it held down while using the starter.
Since you have a diesel it would be better to wait for a day when temperatures are near 32F. The engine will turn over easier and batteries will perform better. You could also use that booster-starter you have,jumped to the starter-battery, at the same time. The more voltage and current to reach the starter, the better.
Trying to start it without access to shore-power would be folly in below freezing temperatures since it did not work at 16F. Forget about rushing things as some have suggested. No use getting all batteries discharged if your attempt fails.
