There is lots of advice from online experts on dealing with a flat battery in a Commodore VY key. The battery is not “user replaceable”, it is embedded inside a key shell that is glued together.
In my case, the battery had leaked.
The following procedure was for the exact key, there may be other key types used in VY production, and it is also possible that other models used a key with the same internals and could be repaired in the same way.
NO WARRANTY: if you break it, you get to keep both parts!
I am an experienced technician, it is inadvisable to attempt this unless you have the necessary competencies.
Enough of the fear, let’s get on with it.
The key uses an ordinary CR2032 lithium cell, though with tabs. Above are two batteries which I prepared with 4mm tabs, but as it turned out, while the +ve one is 4mm the -ve tab is 3mm, I should have used 3mm.
Holden’s answer to the problem of the $2 battery being flat / leaking is to buy a new key head and get it programmed for a total cost of around $150.
Above, the underside of the board. The small chip is a 93S46 EEPROM, which hints that this thing has non-volatile memory and unless the controller chip does something clever like erase the EEPROM on power up, it should be possible to replace the battery carefully without sustaining power to the board.
I purchased two sets of key shells on eBay for about $10, but whilst they looked very nice, the button actuators where too long to be able to close the case and they were discarded.
I reused the original case parts (which had already had the button membrane replaced by after market silicone buttons that failed when it was just a couple of years old – yes another $150 job by Holden standards). I pressed the case together in a soft jawed vice and used a screwdriver to carry a couple of drops of acetone into the join, solvent welding the case. Don’t overdo this, you might want to replace the battery some time in the future.
Be careful breaking into the original key, try not to leave tool marks or crack it, it may be reusable and in my case it was a better fit that the eBay replacement.
I also replaced the rusty M2.5 screws with M2.5x6mm stainless socket head screws (they are about $3/100 on eBay).
All done, and it works fine. It is not waterproof but the original seal didn’t prevent corrosion from leakage of the internal battery!