The logic section of the BL1500 typically dissipates 3 Watt.
The power section has 20 milliohm series resistance inclusive of two series power mos plus traces. Add the contact resistance of the power connectors.
Assuming AWG10 wires it is wise to add another 10 milliohm.
At 30 amp of battery current this means power = 900 x 30 x 10^(-6) = 0.8 Watt.
We can round power dissipation at 4 watt fairly independent of the voltage.