Since I'm vehemently opposed to wasting C batteries on a project with such high current draw, I'm going to use LiPo batteries from the get-go. To make charging easy, I'm going to bundle the cells into packs of three, with a battery protection circuit connected to them to stay safe. Since the circuit adds bulk, I've also purchased 1.25" ID acrylic tube to house them (which based on calculations from another thread should fit snugly with the protection circuit on top). The 11.1v charger to be used has a 5.5x2.1mm jack on it, so I'm preliminarily basing my design around using that. Instead of spring terminals on either side of the pack, it would be easier wiring-wise to have the positive and negative terminal on one end. To do so, I will have to design an end cap that integrates a male plug to attach to the tube, and a corresponding female attachment to add to the battery pack (using shrink-wrap to hold them together).
The only problem I'm facing right now is that this will add on to the length of the tube (which is probably not detrimental), but more importantly, the current ratings of the plugs I'd like to use are only 0.5A@12v. Since measurements on the ROV show a consistent 3A current draw, that would mean a continuous 1.5A would be flowing through each connector, which is 3x their rating. Would it be a better choice to find a different barrel-type connector and simply make a charging adapter, or might it be better to use a totally different method? I'm all for ideas right now, so any input would be appreciated.