What is a battery cycle ?

Plucka

If i discharge my  lithium  battery from 13.8 volts down to 13.1 volts then recharge-is that a cycle or is a cycle fully charged down to fully discharged meaning that I'm doing only 1/2 a cycle roughly. 

mcgivor

Every charge then subsequent discharge would be considered a cycle regardless of depth of discharge, the life expectancy in terms of cycles however would be dependent on depth, the deeper it is discharged the shorter the cycle expectancy and vice versa. This cycle expectancy is largely dependent on the how aggressively the batteries are charged and discharged as well, which can lead to internal damage.

Most posted test results are those done in ideal laboratory conditions, in less than ideal conditions with limited charging windows such as off grid the results may differ significantly, particularly in some chemistries which don't tolerate partial states of charge well. This is compounded by operators who do not fully understand how their particular batteries function, which is why we hear the stories of premature failure all too often.



 

Marc Kurth

And then some batteries need to be charged aggressively in order to stay healthy. Always follow the manufacturer's recommendations.

littleharbor2

Wouldn't a battery at 13.1 volts still have some surface charge voltage from the float charge mode and thus , not actually be discharged at all?

Estragon

Without knowing the chemistry, cell config, and charging stage, a voltage range doesn't really tell the tale.

Assuming FLA, a 13.x range could be no discharge at all, just the battery/charge source in the process of dropping from absorb to float voltage.  

jonr

Not surprisingly, games are played with the definition of "cycle".   IMO, when it comes to battery life, it should always refer to "full cycles", ie it takes two 100->50% partial cycles to be a full cycle.

+1 on the voltage - keep a 12V lead acid battery above ~12.7V and it will experience no cycles.  But that doesn't mean that it will last forever.

Marc Kurth

Generally, manufacturers publish their test results using BCI standard test methods - but there are several. The common tests are the 2 hour and 5 hour discharge from 100% to 0% - not exactly real world for off grid PV, but more typical of UPS systems. In fact they can be misleading if taken at face value without more explanation. Generally, 1.75v per cell is used as 0% remaining charge.

Reputable manufacturers publish curves showing the numbers of cycles at various depth of discharge points,

Remember that the definition of a "worn out" battery means different things to different people. A common value of 80% of original capacity has been heavily for many years, but I am seeing ratings based on 40%, 50% and 65% storage capacity is "end of life." 

mcgivor

Estragon said:

Without knowing the chemistry, cell config, and charging stage, a voltage range doesn't really tell the tale.

Assuming FLA, a 13.x range could be no discharge at all, just the battery/charge source in the process of dropping from absorb to float voltage.  

The battery in question is LiFePo4 from recollection so 13.8-13.1V would represent somewhere in the mid to upper regon of state of charge depending if loads and size thereof are present at time of reading.

Plucka

Sorry Forgot not everybody using lithium batteries..

Dave Angelini

Definitely not everyone! Good and bad with all  battery chemistries. Tailor their attributes and live with their downsides.