Maintenance lube for Aluminum Electra Townie
Cup and cone bearings on a bicycle need 'preload' for them to work properly under load. This is because the balls are tiny spheres of metal that deform under your weight. Hence the bearings must be tightened up slightly beyond feeling smooth when unloaded. Due to quality of parts, i.e. not perfect, a pre-loaded bearing feels 'rough' and requires effort to spin it. There are proper ways of applying the correct pre-load, e.g. with the use of a torque meter, however, 'feel' is a good way to do it. To understand that 'feel', go into a bike shop and try to turn the spindles on the new wheels that are for sale. With rare exceptions all of them will feel rough - this is preload. Now see how your own spindles/axles feel when you turn them without load, chances are that they feel pretty much the same.

If you have rough bearings then you might think the grease is missing. Chances are that it is just the preload and not a grease problem at all. If you are going to dive in there anyway, do get a handle on the preload concept. As for your question on grease, a little grease goes a long way and you don't want it contaminated. The white lithium grease in a tube from your local bike shop will do fine. Yes you can buy posh coloured 'marine' grease but preload is what matters most with bearing setup.