In-Orbit Assessment of Satellite Battery Degradation Based on Electrical Power Subsystem Telemetry

This work presents a telemetry-driven analysis of long-term lithium-ion battery degradation using real in-orbit data from FASat-Charlie, a Chilean Earth observation satellite operating in Low Earth Orbit (LEO) since its launch in 2012 and still active after more than 14 years in space. The study compares two representative mission phases: 2013, considered as the Beginning-of-Life (BOL) due to being the first year with continuous telemetry availability, and 2025, treated as an End-of-Life (EOL) reference corresponding to the most recent complete year of operations.

The analysis focuses on Electrical Power Subsystem (EPS) telemetry, including battery voltage, depth of discharge, charge state, solar array current, power consumption, and battery-related thermal measurements. Telemetry variables with heterogeneous sampling rates are temporally aligned and resampled to a common resolution to ensure consistency across the dataset.

Exploratory data analysis and regression-based metrics are applied to characterize changes in battery behavior over time. Particular emphasis is placed on the evolution of the voltage–depth of discharge relationship as a primary indicator of degradation. In addition, a quarter-based analysis is performed to capture intra-annual variability and operational effects.

Results show measurable shifts in voltage levels, increased dispersion, and changes in voltage–DoD trends between BOL and EOL periods, consistent with aging effects observed in lithium-ion batteries operating in space environments. The proposed approach is fully data-driven and does not rely on detailed battery design models, making it applicable to long-duration and legacy satellite missions that remain operational. This work demonstrates how historical telemetry can support battery health assessment and extended mission analysis for active spacecraft.