Lithium Ion Battery 18650 ageing voltage question

Thread Starter

N11778

Joined Dec 4, 2015
174
Laptop battery pack New. charged by computer 12.48v 4.16v per cell 5 amp hrs
Used battery 1 year 30 cycles. charged manually 13.85v 4.60v per cell 3 amp hrs
All the cells are within 0.03v of each other.
Had to charge the old one manually at 500 ma. the protection ckt in the battery pack shuts
the laptop charger down at 12.7v and says the battery is full.

QUESTION: Does the voltage of a Lithium Ion battery go up as it ages?

All the research I have done says if the voltage is above approx 3.2v the cells are good.
Looks to me like the protection ckt in the battery pack is set to sell battery's.
 

Audioguru

Joined Dec 20, 2007
11,249
You are lucky that your over-charged battery did not explode or catch on fire. The absolute maximum for a fully charged Lithium cell is 4.20V but something caused yours to be way too high at 4.6V. The charger and protection circuit are supposed to limit the charging voltage to 4.20v per cell.

A lithium battery charger is fairly complicated but it sounds like yours is simply a 13.85V power supply that is much too high fed through a resistor. Where is the charge balancing circuit that limits the voltage on each cell? Why didn't the protection circuit disconnect your wrong charging?
 

AlbertHall

Joined Jun 4, 2014
9,670
Had to charge the old one manually at 500 ma. the protection ckt in the battery pack shuts
the laptop charger down at 12.7v and says the battery is full.
It says the battery is fully charged at 12.7V because it is. 12.7V is 4.2V per cell which is the maximum voltage for for such a cell. As Audioguru says you are lucky your manual charging to 4.6V per cell didn't result in smoke or flames.
 
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