Charge time is a function of how many 18650's you are charging, and how 'discharged' your 18650's are. With 2 18650's in the independent slots, the charge current is 750 mA. So to fully charge a 3100mAh cell, about 4.5 hours, with 3400mAh Cells, closer to 5 hours. If you have all 4 slots in the charger in use, the charge current is effectively 375mA, so figure about 8 1/2 hours for 3100mAh cells, and about 9 1/2 hours for 3400mAh cells. However most people recharge before the cell is fully discharged, so your times will be somewhat shorter. YMMV. If you want faster charging times, you might look into an Xtar charger such as the SP2 (up to 2 amps), or VP1 (up to 1 amp). The main drawback of the I4 with 18650's is the long time it takes to fully charge large capacity 18650 cells.