Battery Calendar Aging Calculator

Why calendar aging happens

Li-ion cells degrade electrochemically even at zero cycles—SEI growth, electrolyte oxidation, and electrode interactions continue. Heat and high state-of-charge accelerate side reactions. That is calendar aging, distinct from cycle (throughput) aging.

Model assumptions

Baseline ~2%/year fade at 25 °C and 50% SOC. Rate scales ~2× per 10 °C above 25 °C and rises sharply when average SOC stays above 80–100%. Planning estimate only—chemistries (LFP vs. NMC) and BMS differ.

Storage best practices

For long idle periods: ~50% SOC, cool and dry (15–25 °C ideal), avoid hot garages at 100%. Re-check SoH before returning backup or seasonal vehicles to service.

Frequently asked questions

Q: Include driving cycles? A: No—this is calendar-only; add cycle wear separately. Q: Can SoH recover? A: No—fade is largely irreversible. Q: Cold storage? A: Slows calendar fade vs. hot, but avoid charging lithium below 0 °C.