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].
