The Remora3 requires at least 5V to operate. So 2 x 1.5V Alkaline D cells will not power the device and LiFeS2 batteries are not available in D size - so this leaves LTCs.
It is best to use Spiral Type batteries in the Remora3.
We recommend SAFT LSH20 D Cell batteries due to the required continuous peak current of 400mA.