Quoted from Joydivision:

I remember that style of Eveready batteries form the 80s, so, 30 plus years would be correct. Pretty rare to find a game these days that has been stored for that long, most have been unearthed by now.
The container Gorgar from Germany I bought in 2009 had apparently been in storage since 1985, batteries were out, but with the amount of settled dust, no playfield wear with original shiny factory playfield laquer, original flipper coils & how tight it played seemed consistant with only just a few years of play.
If you want to replace the Backglass at some point, the repros from planetary pinball are excellent.