The battery voltage is not available outside of hte module. The only indicator you have is to check the "battery failed" status bit, which the BIOS does for you and prints the "CMOS battery low" message on POST. If the modules keep time, the battery is not completely depleted. If the modules loose time and report "battery failed", the modules are depleted. That's all you can probe without grinding.

You can grind enough plastic on the battery connection pins that you can probe the battery voltage without disconnection the battery. You can check for battery health that way without making the module unusable in case the battery is fine. If you find 3.2V battery voltage, you modules most likely are NOS.

You can get NOS modules even from non-established sources. I once took the risk, and obtained 2 NOS modules with 1998 datecodes (or the like) from ebay or Aliexpress, and they worked fine. I ground the first of the modules just after seeing the date code expecting a completely dead battery, but instead I found the aforementioned 3.2V. For lithium primary cells at 3.0V nominal, 3.2V means the battery is near 100% state of charge.

Thanks alot. I feared that those Dalles modules are completly sealed units. Mines were from 1995/96 and I assume they are dead or soon to be. If I file them down to the leads I'm halfway done in modifying it. I think I'll modify them and put a coin cell on top.

I've found the easiest way to get into a Dallas is to cut it open with side cutters. That seems to make short work of the top plastic, then cuts easily and controllably into the epoxy stuff.

I always filed above the resp. pins down until I reached the metal. I`ll try your way the next time.