Battery life: DoD, cycles & EoL
How deeply you discharge, how often, and at what temperature decides how long the battery lasts.
A cycle is one full discharge
A cycle counts as one full discharge of the battery's capacity. Two half discharges make one cycle. A LiFePO4 typically lasts 3000–6000 cycles before it loses noticeable capacity; a lead-acid battery perhaps 300–500.
DoD — depth of discharge
How deeply you discharge each time affects the lifespan dramatically. LiFePO4 handles deep discharge down to 20% without trouble. Lead-acid batteries would rather not go below 50% — otherwise the lifespan halves quickly.
- LiFePO4: 80% DoD is fine in daily use
- AGM/gel: stay above 50% for a decent lifespan
- Lithium-ion (NMC): around 80% DoD is common in vehicle batteries
EoL — end of life
Manufacturers state a cycle count down to a given end-of-life percentage — "6000 cycles to 80% EoL", for example, means the battery keeps at least 80% of its original capacity after 6000 cycles. It is not broken, there is simply less capacity left.
Practical life (years) ≈ cycles / cycles per year Example: 4000 cycles / 250 cycles per year = ~16 years
Temperature decides everything
Lithium likes 15–25°C. Never charge below 0°C — it damages the cells permanently. Your battery's BMS should block charging when the cell temperature is 0°C or lower. With a battery that has built-in heating you can charge in the cold too, but bear in mind that the heater warms the battery first before it starts accepting charge. High temperatures (above 40°C) accelerate ageing. Lead loses capacity in the cold but is not damaged as easily.