Everything I have read about Lipo batteries is heat does much more damage to a lipo battery then the cold. Many of the old RC modellers used to keep their lipo batteries in a fridge when in storage believing it slowed down the chemical reaction that destroys lipo batteries.
What might have occured with the battery out in the cold for 2.5 months might be explained here.
Storage induces two forms of losses: Self-discharge that can be refilled with charging before use, and non-recoverable losses that permanently lower the capacity. Table 2 illustrates the remaining capacities of lithium- and nickel-based batteries after one year of storage at various temperatures. Li-ion has higher losses if stored fully charged rather than at a SoC of 40 percent.
View attachment 1800
Table 2: Estimated recoverable capacity when storing a battery for one year. Elevated temperature hastens permanent capacity loss. Depending on battery type, lithium-ion is also sensitive to charge levels.
Batteries are often exposed to unfavorable temperatures, and leaving a mobile phone or camera on the dashboard of a car or in the hot sun are such examples. Laptops get warm when in use and this increases the battery temperature. Sitting at full charge while plugged into the mains shortens battery life. Elevated temperature also stresses lead- and nickel-based batteries.
Simple Guidelines for Storing Batteries
- Primary batteries store well. Alkaline and primary lithium batteries can be stored for 10 years with moderate loss capacity.
- When storing, remove the battery from the equipment and place in a dry and cool place.
- Charge lead acid before storing and monitor the voltage or specific gravity frequently; apply a charge if below 2.07V/cell or if SG is below 1.225 (most starter batteries).
- Nickel-based batteries can be stored for 3–5years, even at zero voltage; prime before use.
- Lithium-ion must be stored in a charged state, ideally at 40 percent. This prevents the battery from dropping below 2.50V/cell, triggering sleep mode.
- Discard Li-ion if kept below 2.00/V/cell for more than a week. Also discard if the voltage does not recover normally after storage.