Coming back to this — raj_pm is right about keeping power on during the swap. I actually got burned by this on a Yaskawa Sigma-5 years ago. Swapped the battery with the drive powered off, lost multi-turn data, had to re-home all 3 axes. Took most of a shift.
Few things I've added to our battery replacement SOP since then:
1. We label every battery with the install date using a Brother label maker. Cheap insurance — you can see at a glance which ones are due without digging through maintenance logs.
2. For Fanuc, the A98L-0031-0012 has a shelf life too. We had a batch of spares sitting in the cabinet for 4+ years and two of them were already below 3.0V out of the package. Now we rotate stock and check voltage before installing.
3. Temperature matters more than people think. Our press near the heat treat furnace eats batteries in about 2 years vs 4+ years on the climate-controlled side of the shop. If your press runs in a hot environment, cut the replacement interval in half.
4. After swapping, I always check the multi-turn counter value against what we recorded at last PM. If it's reset to zero or way off, something went wrong during the swap even if no alarm fired yet.
One more thing — keep at least 2 spares per drive brand on hand. Nothing worse than finding out you need a battery at 11 PM and the only supplier is 3 days out.