It appears to me that the prize Putin is seeking in the south is Mariupol. City with heavy industry and shipyard/ship repair infrastructure.
If that is taken, the subsequent completion of a land bridge, if you will, from Mother Russia to Crimea might be accomplished which would probably achieve some of Putin's goals.
Taking Kiev and installing a more pliant government there would be a "great if we can manage it" goal, but may not be a "have to have" goal.
Or maybe he's decided "all or nothing" and I miss my guess.
In either case, if you can't keep the wheels and tracks rolling, you can't achieve your objectives.
What was it Rommel said about war: "Amateurs talk about strategy and tactics, professionals talk about logistics" (Or words to that effect)
Maintenance and upkeep, and spare parts, fit into logistics.
“The battle is fought and decided by the quartermasters, long before the shooting begins.”