Define "Charge Cycle"

Maybe this is explained somewhere that I've not been able to find but can someone define what a charge cycle is?

Is it every time you charge? Or is it from empty to full, or some % in between? If it's from empty to full, what does a partial charge count as then, a partial cycle?

In terms of longevity, as in the number of usable charge cycles you can get out of a battery pack, does charging a pack every day from 50% to 80% help longevity more than, say, charging every 2 days from 20% to 80%?

In cell tests, a charge cycle is from full to empty, and usually done at a discharge rate a LOT lower than will happen in real world use.

This is part of why you don't get "2000 cycles" from that battery.


In use, a cycle is every time you put it back on the charger. So all cycles are not equal. Generally better to not discharge till very empty, but the rate you discharge often has a lot more to do with battery lifespan than stopping at 80% empty. Stopping at 95% can be a good idea though.

dogman dan said:

In cell tests, a charge cycle is from full to empty, and usually done at a discharge rate a LOT lower than will happen in real world use.

This is part of why you don't get "2000 cycles" from that battery.


In use, a cycle is every time you put it back on the charger. So all cycles are not equal. Generally better to not discharge till very empty, but the rate you discharge often has a lot more to do with battery lifespan than stopping at 80% empty. Stopping at 95% can be a good idea though.

Click to expand...

Thanks.

A cycle for most Li-ions would be 4.20v down to 2.75 or 2.50v (depending on the cell) at a 0.2C (5 hour discharge rate) @ 25C, then the cell is charged back up using a CC/CV charge method to 4.20v with roughly a 50mA cutoff. This is one full cycle. This is how they rate the cell/packs capacity and cycle life generally.

If the pack is charged from 4.20v and discharged by 20% to around 4v then charged back up to 4.20v that would technically be about 1/5th of a cycle. However there are other factors that influence cycle life and cell longevity. The two most important things are to not regularly overcharge or overdischarge the pack. Then another very important thing is to limit the storage of the pack at its fully charged state. Li-ions don't like being left at full voltage (generally 4.20v) for long periods of time. This increases wear on the pack.

My advice would be if you don't need the added range and you only used 20% of the pack, don't charge it. Use more of the pack and then fully recharge it to limit the time the pack stays at a fully charged state.

redilast said:

A charge cycle for most Li-ions would be 4.20v down to 2.75 or 2.50v (depending on the cell) at a 0.2C (5 hour discharge rate) @ 25C. This is how they rate the cell/packs capacity and cycle life generally.
......

Click to expand...

????? ...That is only half a cycle.....the discharge half !
A full "cycle" would end when the cell has been recharged back to 4.2v
Charge rate, temperature, voltage profile, etc , ...all play a significant part in the life expectancy for the cell.

I'm sorry I forgot to say charge it back up to 4.20v, but I think thats pretty obvious to most readers. I've edited the post now to make it more clear.