The 6820 requires two 12V batteries wired in series to provide 24 VDC (Page 29) [1].
The system has a charging capacity of 7 to 35 AH, though the internal cabinet only holds a maximum of two 18 AH batteries (Page 4, 29) [1].
For battery requirements up to 35 AH, an RBB accessory cabinet must be used (Page 29) [1].
Batteries must be of the same AH rating and should never be wired in parallel (Page 29) [1].
It is recommended to replace them every five years (Page 25, 29) [1].
