Purchasing new batteries: How do you determine what one 'cycle' is?

[max2k]

DoD vs life chart (suggestion only, your mileage will be less)


Battery-DoD-vs-Cycles.gif

is this for AGM? 50% DOD gets you only 1.3 years of daily use.

[Mike90250]

DoD vs life chart (suggestion only, your mileage will be less)


Battery-DoD-vs-Cycles.gif

[tombarton]

Thanks guys for all the info. Illuminating stuff and really helpful with planning.

I recognise now that a cycle is a cycle, but how many of these constitute a battery's lifespan depends on the average DOD over this lifetime.

[NEOH]

How do you determine what one cycle is?

Assume nothing when it comes to, what is a cycle or the number of deep cycles, for a deep cycle battery.
One cycle is a discharge and then a charge, regardless of Depth of Discharge.
Now, how many of those deep cycles you get is dependent upon the average % Depth of Discharge, of each and every cycle, and also the battery's age.

You may get ...
1,500 Cycles at 20% Depth of Discharge - a shallow cycle
750 Cycles at 40% Depth of Discharge - a medium cycle
375 Cycles at 80% Depth of Discharge - a deep cycle

As you can see from above ... what is a Cycle does vary.
And so the number of cycles must always be stated with the "% Depth of Discharge per Cycle" to be meaningful.
Typically, the actual lab testing parameters used per CYCLE is not specified.
The graph for "Number of Cycles vs Depth of Discharge" is FOR ESTIMATION PURPOSE ONLY - meaning you will get less.

[Mike90250]

I've understood 1 cycle to be about a 20% change in charge level. Full down to 80% and recharge back to Full would equal 1 cycle. If you only go down 10%, it's not a full cycle but does add to age. Often, there is a Depth of Discharge vs Cycle life, and you can look at ways to maximize your investment,

[max2k]

Hi all, I'm looking to purchase new SLA batteries for an off-grid system. I know I need to choose something with a high number of cycles, so that it will be well-suited to the task of daily use and recharging.

My local solar shop sells some AGMs with a lifespan of around 350 cycles. At first I thought this was too low to even last a year, but then realised a 'cycle' likely does not just mean one day of drawing and one day of charging, but that in this context one 'cycle' may mean an entire capacity use/charge. In this case, the battery could last several years' usage.

Can someone please shed some light on what constitutes a 'cycle' for this purpose, and how to calculate the potential lifespan of a new AGM battery?


*Note to noobs: I learned the hard way, and was one of those people who bought some used UPS batteries to 'save money'. Turns out they have an extremely low number of cycles, as they're designed to live on float charge and give all their energy in emergency situations, as opposed to being constantly run down and recharged as expected in a solar setup.

If you really going to charge/discharge them daily- take a look at LFP cells, much better deal in the long run IMO: 20x cycle life + 1.5 times more energy for the same Ah and other stuff I mentioned in your other thread. After 1000 cycles at 0.5C current it will still have 90% original capacity: LFP_Cycle_Life.jpg

[tombarton]

Hi all, I'm looking to purchase new SLA batteries for an off-grid system. I know I need to choose something with a high number of cycles, so that it will be well-suited to the task of daily use and recharging.

My local solar shop sells some AGMs with a lifespan of around 350 cycles. At first I thought this was too low to even last a year, but then realised a 'cycle' likely does not just mean one day of drawing and one day of charging, but that in this context one 'cycle' may mean an entire capacity use/charge. In this case, the battery could last several years' usage.

Can someone please shed some light on what constitutes a 'cycle' for this purpose, and how to calculate the potential lifespan of a new AGM battery?


*Note to noobs: I learned the hard way, and was one of those people who bought some used UPS batteries to 'save money'. Turns out they have an extremely low number of cycles, as they're designed to live on float charge and give all their energy in emergency situations, as opposed to being constantly run down and recharged as expected in a solar setup.