Tom,
OK yes now I see where you are.
That is not telling you that you have a low battery.
You should only have the coin battery on the MPU it should be above 2.9V
Hopefully you have already removed the varta battery, 500 series or 1270.
Battery 2 is not for the one in the top box.
Are you having a specific problem? Is the VFD indicating a low battery? If it is you need to change the coin battery on the lower cpu.
If the top box battery goes bad and it is a bios 2 top box you will get an indication on the top box boot screen about cpu speed has changed.
Bios 1 can run with a dead top box battery.
Rich