Glossary
Battery cycle
A battery cycle is the equivalent of one full charge followed by one full discharge. Two 50% discharges count as one cycle. Solar battery warranties are stated in cycles or years (whichever comes first) and in the percentage of capacity the battery will retain at the end. Each cycle wears the battery slightly; how it is used decides how long it lasts.
What a cycle is
Every time a battery charges and discharges, its chemical components suffer a bit of wear. That wear accumulates and capacity slowly declines. The cycle is the unit for counting it. It does not have to be 0 to 100: the industry adds up partial discharges, so using 30% in the morning and 70% in the evening equals one full cycle.
A battery cycled daily to shift consumption (charge from solar at midday, discharge at night) runs about 365 cycles a year. One used only as outage backup may run a dozen. The same battery lasts very different numbers of years depending on that use.
Why it matters in Florida
With 1-to-1 net metering, cycling the battery daily makes no economic sense in Florida: the grid credits your surplus with no wear. That means a battery installed as backup runs few cycles, and its life is set more by heat and time than by use. If instead you are on a time-of-use rate and discharge every afternoon, cycles climb and the cycle warranty becomes the number that matters.
LFP chemistry tolerates far more cycles than earlier ones, which is why it dominates the residential market.
Common mistake
Looking only at warranty years. Two batteries with ten-year warranties can differ in the cycles covered and in the capacity they guarantee at the end (for example, retaining a certain percentage of the original). Ask for all three figures: years, cycles and guaranteed end-of-warranty capacity. We explain it in how long solar batteries last.
Updated