For those that only need backup for 1 device, Schneider / APC has (had?) a product called APC Connect that is able to supply up to 33 watts for up to 12 hours.
Another option if you only need to backup the Tablo itself is to use a ‘Belkin Residential Gateway Battery Backup Rev B Model BU3DC001-12V’. These can be found quite inexpensively on eBay: Bu3dc001 | eBay
I doubt this will give the same 12 hours runtime that is stated for the APC Connect, but it should last several hours & is much less expensive.