The risks of using steel cable for power are going to be corrosion/rust. The primary way this will cause problems is around connections, but long term it is also an issue away from connections. At connections, corrosion can cause the wire to become loose, something like ox-gard can be used to delay this significantly. It isn't designed for steel but some kind of protection must be done at connections or arcing will be a major risk. Longer term the wire itself will rust, and at some point the conductive cross section of the wire will be compromised to the point it overheats and melts. This might be a year and it might be 100 years depending on factors which are hard to predict and control.

TLDR: connections must be protected by some kind of anti oxidation coating, if you have nothing else use grease but something designed for electrical connections is better. If you have nothing else, melt some lead and dip the exposed part of the wire in that to coat it. Lead should be readily available in a war zone? Long term the wire WILL melt at some random point along the wire so it is much better if this wire is kept away from anything flammable.