# Efficiency of charging a lithium ion battery with a lithium ion battery

Should I need to charge one lithium ion battery with another, what sort of loss would be typical?

If I had a 65wh battery, can I calculate how big a battery I need to charge it taking into account the loss?

• What interconnecting charger circuit would you use and how energy efficient is that circuit? Commented Jun 6, 2020 at 10:04
• I do not know, I am looking generally at so called "power banks" to charge an internal laptop battery. Commented Jun 6, 2020 at 10:07
• This is rough - many variables: If you use a power-bank and then a charger you get efficiency of PB x efficiency of charger x efficiency of battery process. I'd guesstimate 90% for each, or less. So 0.9^# ~= 70%. || If you integrate the the first two in a battery to charger stage you can expect maybe 80%. | Note that LiIOn CURRENT charge efficincy is 99%++ but energy charge efficiency is less. look at Vcgg profile with time. Towards the end of CC mode Vghg rises at a higher rate for same current. Efficiency drops in this region. Commented Jun 6, 2020 at 10:28
• Vghg -> Vchg -> Vcharge Commented Jun 6, 2020 at 11:11
• Thanks, that helps alot. Commented Jun 6, 2020 at 11:23