Cycle Life

What counts as a cycle

A full cycle is one complete discharge and recharge - from whatever the usable maximum is, down to the discharge floor, and back. In practice, most home batteries don’t cycle fully every day. A partial discharge (say, 50% depth) counts as half a cycle in most warranty calculations.

Manufacturers typically quote cycle life at a specific depth of discharge. “6,000 cycles at 80% DoD” means: cycle to 80% depth 6,000 times, and the battery should still hold at least the warranted minimum (usually 70% of original rated capacity). Cycling to shallower depths consistently will yield more total cycles - which is why batteries with built-in DoD limits often outlast their warranty projections in moderate climates.

Turning cycles into years

At one full cycle per day:

• 3,650 cycles = 10 years
• 6,000 cycles = 16.4 years
• 10,000 cycles = 27.4 years

Most residential storage warranties combine a cycle count with a time limit (whichever comes first). BYD’s Battery-Box, for example, warrants 10 years or 6,000 cycles at 80% DoD to a minimum of 70% capacity. Sungrow’s SBR series covers 10 years with a guaranteed throughput figure rather than a cycle count.

Because a home battery cycling once per day will hit the time limit well before the cycle limit in most cases, the cycle life figure is more relevant for commercial applications or systems used for grid services where cycling happens multiple times per day.

Chemistry matters

LFP (lithium iron phosphate) significantly outperforms older NMC (nickel manganese cobalt) chemistry on cycle life. NMC cells used in early home batteries (some 2015–2018 products) were typically warranted to around 3,000–4,000 cycles. Most residential LFP products now carry 6,000+ cycle warranties, and some claim 10,000+ under specific conditions.

The trade-off is energy density: LFP cells hold less energy per kilogram than NMC, which is why EV manufacturers still use NMC for long-range vehicles where weight matters. For a stationary home battery bolted to a wall, energy density is irrelevant - cycle life and safety are the metrics that count.

Calendar ageing

Cycle life doesn’t capture the full picture. Batteries also degrade from sitting - even if rarely cycled. High temperatures accelerate calendar ageing, which is why Australian installations should keep batteries out of direct sun and away from poorly ventilated spaces like hot roof voids. A battery in a cool garage will consistently outlast the same model installed in an unshaded outdoor enclosure in northern Queensland.