# Importance of the constant voltage charging of li-ion

Hello everyone is it necessary to have the constant voltage (CV) process when charging 18650 li-ion batteries?

What happen if I usually skip the CV? Does the li-ion battery got memory? I know the CV is needed to charge the battery full but it's really time costing. Thanks

If you use CC until Vcell is ~= 4.2V then.

• Cell capacity will be about 80% of maximum

• Charging time will be about 45 minutes.

• Cell whole of life capacity stored and recovered will be signifixantly higher due to the gentler charging cycle.

4 hours should be very adequate for a full charge at I max = C.ie Imax =~ 3.2A for 3200 mAh cells. The CC stage will last about 45 minutes leaving 4h-45m = 3h-15m for the CV stage.

If you search SE EE for LiIon charging you will find this area is well covered.

• Thank you very much but I got confused with the third point does it means if I usually skip the CV and in one day I wnat to charge it full then I should use lower current to charge? Thanks Jun 25, 2018 at 14:50
• 3. Using CC only result is as 3 above. If you follow with CV the cell will set what current it draws. For a fullish charge terminate at I = Imax/2. For more charge terminate at Imax/4. For road warrior very charged use Iterminate = Imax/10. As Iteminate is increased battery life is increasingly reduced. Jun 28, 2018 at 8:01

Some chargers skip the CV phase for a really 'fast charge', and show 'charge complete' once it reaches terminal voltage. However, it's still not fully charged at that point, and can accept a bit more. If you drove in that last bit of charge as quickly as in the CC phase, then you'd damage the cell by over-volting it, the CV phase is to avoid this damage.

The question is, do you want to use a mostly charged battery very quickly, or do you want to use a fully charged battery but wait a bit longer for it? The choice is yours. It's not necessary to do it either way.

• Thank you for your help. I need to use 3-4 3200mah 18650s everyday during my work and the worst situation I back home at 7:30pm and need to sleep at 11:30 therefore only 4 hours are available to charge the batteries. According to your info then I can only charge the CC if time is not enough and I already got approx 80% of the capacity. And this will not affect the battery in long run as li-ion dont have memory 😁😁 Jun 24, 2018 at 10:19
• @user186819 Two observations. Four hours ought to be more than enough to accomplish both CC and CV phases, mine are usually fully cooked in an hour. Jun 24, 2018 at 11:32
• @Neil_UK IF you charge at C then 1 hour is too little for CC + CV chaarge except if the CV terminates at a very high current. eg CC at C for about 70-80% of capacity until V reaches ~= 4.2V is 70-80% x 60 minutes = 42 to 48 minutes. That leaves 12 to 18 minutes for the CV tail - which is rather short if Iterminate is say C/10 oir C/4 but MAY be reached if Iterminate is C/2 or higher.. Jun 24, 2018 at 11:56
• I'm planning to charge at 1.5A x4 as this is the maximum output of my charger. 3200/1500=2.13 just hope approx 2-3 hours will be finished. 😁 Jun 25, 2018 at 14:45