Question re: Li-ion Capacity vs. Voltage

[Atomic_Chicken]

Greetings!

Does anyone here have the figures for Li-ion capacity vs. measured voltage? Ex: 100%=4.2V, 90%=4.1V, etc.)? Also, is this voltage measured open-circuit, or does a small load need to be applied during measurement?

Best wishes,
Bawko

 

[cy]

li-ion voltage/capacity is measured without load. it's almost a linear drop.

Silver will have the exact numbers. general rule of thumb is to charge to 4.1v for most cycles. then when you need max capacity charge to 4.2v.

depending upon mfg tolarance is +/- .5v from 4.2v. factoring for meter error and most low end charger don't always terminate at 4.2v. it's best to not go over 4.2v

when cell drops to 3.5v for all practical purposes cells is empty. there's so little energy to be gained draining to 3.0v it's not worth the risk of cell.

for bare li-ion cells, best to yank cell at first sign of dimming. then quickly measure voltage a few cycles to know where cell is at. goal is to yank cell before it drops below 3.5v.

 

[SilverFox]

Hello Bawko,

We have been "playing" with this formula, and it seems to be representative. The voltage you put into the equation is resting voltage. This is good down to around 3.8 volts, which is about 40% of a full charge. The state of charge verses voltage below 40% seems to vary with battery manufacturer, but above 40% seems to be quite consistent.

SOC% = 100(0.1966+SqrRt(0.0387-1.4523(3.7835-CellVoltage)))

Have fun.

Tom