I'm struggling to find the reason for the battery backup / UPS. It has to be charged occasionally by the system, so doesn't make it's consumption zero standby.

I'm struggling to find the reason for the battery backup / UPS. It has to be charged occasionally by the system, so doesn't make it's consumption zero standby... Why not drive the circuit directly from the A/C via a DC transformer? Is it to keep the memory of the last cycle to not over cycle the compressor?