Backup batteries are optional, but recommended. Assuming 12VDC, the operating current of a Smart Hub ACU is 1 Amp and a Smart Reader is 0.25 Amp. To power a Smart Hub ACU and four readers, you'd need 2 Amps. And if you're powering locking hardware, you'll need to take that into consideration too. A fully loaded system (ACU, readers, and locking hardware) is about 4 Amps times the number of backup hours needed. To keep the system running for 3 hours with all entries engaged, you’d need a 12V 12Ah sealed lead acid (SLA) or gel cell battery.
Note: For a 24V power supply, you need two 12V SLA or gel cell batteries in series.
Your installer can help you determine the right backup battery for you.