We have customers that transmit power over a mile. What we usually do for this is use a generator that produces a higher voltage such as 120 or 240. This is sent using three wires (it is three phase power) to a transformer panel at the batteries. This steps down the power to battery voltage and then a rectifier converts the AC power to DC. Using transformers is an economic decision as it may be cheaper to use larger wire and transmit the power at battery voltage. This is also simpler than transformers.