Battery Lifetime and Cycle Life: What Determines How Long Batteries Last

One of the most common questions in battery selection: ‘How long will it last?’ The honest answer depends on usage patterns, maintenance, and operating conditions. Here is the complete picture.

Calendar Life vs Cycle Life

• Calendar life: Years of service regardless of use. Battery degrades even when stored charged.
• Cycle life: Number of charge/discharge cycles before capacity drops to 80% of original.
• Battery reaches end of life when either calendar life or cycle life limit is reached.

Factors That Kill Battery Life

1. Depth of discharge: The biggest factor. Discharging to 100% DoD cuts life dramatically vs 50% DoD
2. Temperature: Every 10C above 25C halves float life of lead-acid
3. Chronic undercharging: Batteries that never reach full charge develop permanent sulfation
4. Overcharging: Excessive voltage causes grid corrosion and water loss
5. Vibration and shock: Physical damage to plate structure
6. Age: Even unused batteries degrade over time (calendar aging)

Battery Life by Technology

• AGM: 4–8 years float, 400–700 cycles @ 50% DoD
• Gel: 6–10 years float, 600–900 cycles @ 60% DoD
• OPzV tubular GEL: 15–20 years float, 1,200–1,500 cycles @ 80% DoD
• LiFePO4: 10–15 years, 3,000–6,000 cycles @ 80% DoD

Calculating Realistic Battery Lifespan

Example: OPzV battery in a solar system cycling 1x per day at 50% DoD:

At 50% DoD, OPzV achieves approximately 3,000 cycles.

Lifespan = 3,000 cycles / 365 days = 8.2 years

If used at 80% DoD: 1,500 cycles / 365 = 4.1 years

Conclusion: Operate at 50% DoD to maximize years of service from OPzV batteries.