Why Is My Tesla Battery More Degraded Than Others With Similar Mileage?

Tesla owners often assume that if their vehicle isn’t driven frequently, their battery isn’t deteriorating. In reality, lithium-ion batteries experience degradation even while stationary. A phenomenon known as calendar aging. Calendar aging encompasses all gradual battery degradation processes that occur during periods of inactivity, independent of active driving or charge-discharge cycles. One of the most critical factors influencing calendar aging is the State of Charge (SOC): leaving a battery at a high state of charge, especially fully charged, for extended periods, can significantly accelerate capacity loss, even if the car remains parked and unused. This explains why my Tesla battery has experienced greater degradation compared to other vehicles with similar mileage, as illustrated in Figure, which also accounts for battery replacement. 

To clarify the impact of parking your vehicle at high SOC, we reviewed several peer-reviewed experimental studies from top-tier journals such as Journal of Power Sources, Journal of The Electrochemical Society, and ChemElectroChem as shown in the following table.

The findings consistently show that higher storage SOC causes faster capacity loss, especially when combined with elevated temperatures. This degradation happens even if the vehicle is not being driven.

• At 90–100% SOC, lithium plating, SEI growth, and electrolyte oxidation are accelerated.

• At 20–50% SOC, the chemical environment inside the battery is more stable, resulting in significantly lower degradation rates.

• Studies confirm that degradation due to SOC is nonlinear—there is a sharp increase in wear as SOC crosses ~90%, especially in NCA chemistries.

Study	Battery Type	SOC Tested	Storage Temp	Key Results
Keil et al. (2016) [1]	NCA, NMC, LFP	0–100% in ~10% steps	25 to 50 °C	Capacity fade increased sharply above 90% SOC for NCA; NMC showed accelerated aging at 100% SOC.
Hahn et al. (2018) [2]	NMC/Graphite	0–100%	40 to 55 °C	Capacity loss at 100% SOC was significantly greater than at 30–50% SOC.
Liu et al. (2020) [3]	NCA	20%, 50%, 90%	10, 25, 45 °C	Higher SOC and temperature accelerated degradation. 90% SOC cells degraded faster than 50% or 20% SOC.
Frie et al. (2024) [4]	NCA (Ni-rich 18650)	~20% vs ~80%	50 °C	After 10 months, ~80% SOC lost 11% capacity vs 7% at ~20% SOC—about 50% more degradation.
Geisbauer et al. (2021) [5]	NCA, NMC, LFP, etc.	2%, 38%, 100%	18.5 to 60 °C	NCA cells stored at 100% SOC and 60 °C degraded by up to 30% in just 120 days.

Dr.EV actively monitors your real-world driving patterns, distinguishing between daily commuting habits and occasional longer trips. By continuously analyzing factors such as typical mileage, frequency of longer journeys, and environmental conditions, Dr.EV intelligently determines the most suitable SOC limits for your specific usage. Unlike rigid manual methods, Dr.EV’s SOC recommendations dynamically balance optimal battery care with practical usability:

• Reduced Degradation:

  By avoiding prolonged periods at high SOC, the AI recommendations significantly slow calendar aging, preserving your Tesla’s battery life.

• Minimal User Inconvenience:

  You get maximum battery protection without sacrificing flexibility or driving comfort.

Summary for each paper:

Keil et al. (2016) conducted a comprehensive study published in the Journal of The Electrochemical Society, analyzing the calendar aging behavior of NMC and NCA lithium-ion cells. Cells were stored at various states of charge (SOC), ranging from 0% to 100%, for approximately 9–10 months at temperatures between 25°C and 50°C. Their results showed a non-linear relationship between SOC and capacity fade: degradation remained low across moderate SOC ranges but increased sharply at high SOC levels. Specifically, NMC cells exhibited significant accelerated degradation at 100% SOC, while NCA cells began to show notably increased aging only above approximately 90% SOC. The authors concluded that battery life could be substantially prolonged by avoiding storage at high SOC levels.

Hahn et al. (2018) investigated the calendar aging of NMC/graphite cells, publishing their findings in the Journal of Power Sources. Cells underwent long-term storage under different SOC and temperature conditions. Their quantitative analysis clearly indicated that higher SOC directly contributes to faster capacity degradation, with elevated temperatures further intensifying the aging process. For instance, cells stored consistently at 100% SOC degraded significantly faster compared to those kept at lower SOC (30–50%) under identical temperature conditions. This outcome aligns closely with other studies, such as Naumann et al. (2018) on LFP cells, reinforcing that accelerated calendar aging at high SOC is consistent across various lithium-ion battery chemistries.

Liu et al. (2020) conducted an extended 435-day storage experiment specifically on NCA cells, relevant to Tesla’s battery chemistry. Their study, published in Renewable and Sustainable Energy Reviews, evaluated cells stored at 20%, 50%, and 90% SOC at three temperatures (10°C, 25°C, and 45°C). They observed a distinct correlation between increasing SOC and accelerated battery degradation at all tested temperatures. At room temperature (approximately 25°C), cells stored near 90% SOC showed noticeably higher degradation compared to those stored at 50% or 20% SOC over the same period. Elevated temperature (45°C) further amplified degradation rates, clearly demonstrating that maintaining lower SOC levels during battery rest periods effectively preserves battery health.

Frie et al. (2024) presented a noteworthy long-term study in ChemElectroChem, tracking the calendar aging of Ni-rich NCA (graphite-silicon anode) lithium-ion 18650 cells over an unprecedented five-year period. In their findings, after approximately 10 months of storage at 50°C, cells maintained at around 80% SOC experienced approximately 11% capacity loss, compared to just 7% capacity loss for identical cells stored at approximately 20% SOC. The substantial 50% greater degradation observed at the higher SOC underscores the significant impact of maintaining batteries at elevated charge levels, particularly under warm storage conditions, further emphasizing the importance of controlled SOC management.

[1] P. Keil et al., “Calendar aging of lithium-ion batteries,” J. Electrochem. Soc., vol. 163, no. 9, pp. A1872–A1880, 2016.

[2] S. L. Hahn et al., “Quantitative validation of calendar aging models for lithium-ion batteries,” J. Power Sources, vol. 400, pp. 402–414, 2018.

[3] K. Liu et al., “An evaluation study of different modelling techniques for calendar ageing prediction of lithium-ion batteries,” Renew. Sust. Energy Rev., vol. 131, p. 110017, 2020.

[4] M. Frie et al., “Experimental calendar aging of 18650 Li-ion cells with Ni-rich NCA cathode and graphite-silicon anode over five years,” ChemElectroChem, 2024, Early View.

[5] C. Geisbauer et al., “Comparative study on the calendar aging behavior of six different lithium-ion cell chemistries in terms of parameter variation,” Energies, vol. 14, no. 11, p. 3358, 2021.