Bad memory battery, possibly, if it loses the data when the main battery is disconnected or discharged. I downloaded the 580 service manual from the internet as a pdf file, so just search for it. If you cannot find it, contact me at email@example.com
, and I'll e-mail it to you.
It is replacable, and the manual shows where and how.
Finding a battery with the little metal tabs spot welded on will be the most diffcult part of the project. so just make your own.
The cell that's there is a common lithium button cell available at most drugstores. When I do these, I just clean the cell with scotchbrite, use a hot 15 watt iron and kester 88 solder. Place the cold solder on the cell, and melt through it with the iron. Hold for maybe 2 seconds. Do both sides. That tins the cell. Next, strip and tin 2 ea. 1 inch long 20 ga. solid wires. Quick solder the wire ends. If you like to be fancy cover the cell with some heat shrink tube. Use this cell just as the factory cell. You can salvage the metal strips from the old cell by breaking them off using pliers and a rolling motion, flattening them out, tinning, and soldering them on, but for me, that takes too long.
Pay attention to the polarity...., mark the battery and board + and -, remember which lead is + and -.
Before you solder it in, be sure your soldering iron has no floating voltage on it, and use a jumper lead and a 1K series resistor to ground it to the radio when soldering the battery in. Why the resistor? If one side of the new battery is grounded, you short it out with the grounded iron when soldering the hot side. The 1K resistor is low enough to dump off static charges, but not high enough to do anything to the new cell.
I have replaced cells in older Kenwood VHF mobiles, My Dj-820 (rebuilt the 12V battery with Maha Nimh's as well), Icom 735's, various meters, even the cell in the voltile memory of my Icom 751. Never an issue. If you want to save the memory (like the icom 751) use 2 AA, c's or d's cells in series, and 2' of thin wire for hookup, and temporarily tack solder it to another circuit board location to supply power while the button cell is out. This is how I did the Icom.