What batteries does the 5820XL use, and when is an external battery cabinet required?

The 5820XL uses two 12V batteries (Gel Cell or UL listed) wired in series to provide 24V, with a total charging capacity of 7.0 to 35 AH (Page 36, 41) [1].

An external RBB Accessory Cabinet is required if the backup batteries exceed 18 AH, as the main control panel cabinet is limited to an 18 AH maximum (Page 2, 37) [1].

Although one specification sheet lists a 7 AH limit for the main cabinet, the primary installation sections specify 18 AH (Page 14) [1].