18-24 Hours Of Battery Backup

What are my options for powering a camera system with an NVR pulling 30 watts and 3.8 peak watts from 13 cameras.

Just to keep things rounded I have been going with 75 or 100 watts of draw.

Seems like something like this could cost 1000's?

Originally they were requesting 2 full days of backup.

The customer who is inquiring "says" that at their other house, 2000 miles from me, that company has an "intricate" system with what appears to be two car batteries. Any ideas?

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