Mech mods do not regulate voltage or wattage. Whatever voltage is in your battery is what is applied to your coil (roughly, there is some loss as current flows from battery to coil due to natural resistance of tube, switch, 510 connection, etc.). As BrandonR noted, most fully charged batteries start at 4.2 volts. As you vape, this will decrease. Ohm's law tells us power (wattage)=voltage squared/resistance. So your watts mainly depend on the resistance of your coil build, and how much life is left in your battery. Wattage will gradually decrease as your battery drains.