The Solo packs 4400 mAh with its two Li-Ion 18650 3.7v 2200 mAh batteries
you can either add the voltage or add the current, but not both. 3.7v is too low a voltage to power a vaporizer (for herb), so the solo puts the two cells in series = 7.4v @ 2200 mAh. 6.6v @ 3300 mAh only lasts about 70 minutes, ime.