It depends on the size of the load.

Just FYI, every building that is required by law to have emergency backup power has an engine-generator set. There are zero exceptions to this rule. If batteries were able to serve critical loads like hospitals and emergency dispatch centers, they would be allowed to be installed for that purpose, but they aren’t. This should end the argument about battery backup, at least until battery storage density reaches a point where it can serve those loads.

FWIW I sell and run electrical work

To add, grid-scale batteries do make sense if you have a ton of cheap land. Most facilities that need backup power aren’t in areas with lots of cheap available land for battery installations.

The kind of backup power needs that hospitals, data centers, and other critical facilities have (multiple MWH per hour at minimum for large facilities) and the durations they need to operate for, combined with the land prices in the areas where they are situated, make battery backup for critical power needs uneconomical due to the space needed with current battery energy density.