Just adding something that I understood
:
on the back of the 900AMP box it says:
Battery Power: 12V ,
17AH.
AH= Ampere hour.
The HEQ5 uses 2.5 ampere per hour.
The battery will last 17/2.5 = 6.8 hours if only the mount runs from it.
Each additional device will suck it dry faster.
(Here is a tiny question mark! --> ? )