While running the T-Beam node for overnight data collection in my car, I initially used a 1P 3S battery pack built from LG 18650 cells manufactured in 2014. Despite matching cell voltages at full charge and rebuilding the pack twice, I consistently observed that one cell would drop below minimum voltage during overnight runs. This was especially prominent during cold conditions, with ambient temperatures reaching as low as 16°F (-9°C).

The failure pattern repeated: one cell would underperform and trip the pack, even after manual voltage balancing. This behavior is consistent with aged lithium cells showing increased internal resistance and reduced cold-weather capacity.

After two failures, I replaced the pack with a drone battery rated at 3000 mAh, consisting of two 1500 mAh 3S packs wired in parallel. These cells are newer (purchased this year), were always run in parallel from the start, and appear to be well balanced. Since switching, the system has remained stable and reliable during cold overnight use.

This confirms the expected behavior of degraded lithium-ion cells in cold conditions, especially when not capacity-matched. Future deployments will prioritize newer, pre-matched packs rated for temperature and discharge consistency.

-RR