Depends upon the wattage setting you plan to use. Are you using a single, dual, or triple battery mod? In the interests of keeping things simple:
-If you use a good quality 15 amp CDR battery like the Samsung 30Q or Sony VTC6, then you are good up to 45 watts per battery; 90 watts using two; 135 watts for three batteries.
-If you use a good quality 20 amp CDR battery like the LG HG2 or Samsung 25R then you are good for 60 watts per battery. If using a 2-battery regulated mod, your good for 120 watts as you have two batteries. If you are using a 3-battery mod, you're good for 180.
-If you use a single 25 amp CDR battery like the Sony VTC5A, then you are good for 75 watts per battery, 150 watts for two batteries, and 225 watts with three.
-If you use a single 30 amp CDR battery like the LG HB6 you are good up to 90 watts; with a pair of 30 amp CDR batteries you could safely do 180 watts.
WATTAGE PER SINGLE BATTERY:
20W-45W:
Samsung 18650 30Q, 3000 mah 15 CDR
Sony 18650VTC6 3000mAh 15 amp CDR
20W-60W:
LG 18650HG2 3000mah 20 amp CDR
LG 18650HE2 2500 mah 20 amp CDR
Samsung 18650-25R, 2500 mah 20 amp CDR
Sony 18650VTC5, 2600 mah 20 amp CDR
Sony 18650VTC4, 2100 mah 23 amp CDR
AW 18650 3000 mah 20 amp CDR
30W - 75W:
LG 18650 HD4 2100 mah 25 amp CDR
LG 18650 HD2 2000 mah 25 amp CDR
Sony 18650VTC5A, 2500 mah 25 amp CDR
60W - 90W:
LG18650HB6 1500mah 30 amp CDR
LG18650HB2 1500mAh 30 amp CDR
LG18650HB4 1500mAh 30 amp CDR