There was a more technical discussion about remote battery boxes buried in this thread.
https://community.tempest.earth/t/sky-solar-battery-charge-conversion/1272
One of the big concerns pointed out in that thread is the lack of power conditioning on a long, unshielded power wire when exposed to nearby lightning strikes or the RF power from that pesky ham radio operator in the basement sending out a 1,000+ watt CQ. 
There is also a picture of my butchered-up Sky mounting adapter that taps the external power pads for whatever you want. Just make sure to take the batteries out of the Sky, or bad things may happen due to the lack of charge circuitry or protection…