That is amazing that the batteries did not leak and still show a charge. As others have experienced,I've had to repair damage caused by batteries that have leaked during storage.
I stopped at a garage sale a few weeks ago and found a Blue Point CGA-8B Automotive Electrical Tester.Turns out the elderly gent having the sale had operated a service garage years back and had some old stock he was selling off.There was nothing I needed,but I spotted the tester and he said I could have it for $10.00.The meter movement was good,It had the manual and test leads still with it,so I bought it.
When I got it home I cleaned it up a bit and upon opening it up found it still had the original battery in it,(still wired in place from the factory).The tag secured with the wire said,"Wired fo shipping only.Remove when replacing battery." The battery had leaked and caused a bit of a mess,but I was able to clean it up and after installing a new battery found the tester to be still functional...The shadowing on the photo of the manual is fom overspray -the fellow's son does auto body and paint .