From BMS specification page
Mewyeah
Working power: 0.15A * 24hrs = 3.6Ah
Output control drive current listed at 0.5A could be a limitation and if so that could explain the 5 relays shown in this photo: (Note: Just my guesses below, please correct if wrong.)
ecotrek relays.jpg
Looks like:
1 & 2 are contactors (heavy duty relays)
3, 4 & 5 are automotive type relays
The drive current for the contactors could be 1.5A or more. If so, each would need an automotive type relay. BMS controls small relays which in turn controls a large contactors.
The 5th relay,
not necessarily #5 in the photo, could be the heater control relay.
If you add it all up:
0.15A + <0.5A + <0.5A + >1.5A + >1.5A = 4A or so.
Also, 40W heaters if needed so another <4A including relay. The relays and contactors would give off heat too.
Plus there appears to be two small modules that would use power.
Note: Just my best efforts guessing at what's in the box and what it's for.