When I installed relays and higher wattage bulbs, I measured voltage loss from the battery to the lights.
Stock lights, 55/60 Amp, stock wiring, 13% voltage loss low beam and 18% high beam. Thats 1.6 and 2.2 volt loss....
Stock lights, 55/60 Amp, upgraded wiring and relays, 2% and 2%.
Hella ecodes, 80/100 Amp, upgraded wiring and relays, 3% and 4%.