This report covers the critical cold-weather performance testing conducted on November 10, 2025.
- Test Environment: Outdoor, snowy conditions. Ambient temperature was 1°C, feels like -4°C.
- Test Objectives:
- Validate the self-heating function when charging in below-freezing conditions.
- Validate the battery's ability to discharge high amps while cold.
- Perform a deep discharge test to find the 0% SoC shutdown point and observe voltage performance under load.
Test 1: Self-Heating (Cold Charge) Data Log
Objective: To validate the self-heating function. The battery was at a "cold soak" state.
| Time | SoC % | Volts (V) | Amps (A) | Temp (°C) | Heater Status | Warnings/User Notes |
|---|---|---|---|---|---|---|
| 15:23 | 65.4% | 13.3V | 0A | 1.1°C | Off | "Charge Low Temp Protection" Active |
| 15:26 | 65.4% | 13.1V | -8.9A | 1.1°C | Off | (Small load from trailer systems) |
| 15:27 | 65.3% | 13.74V | +35.5A | 1.1°C | ON | TEST START: Shore power applied. Heater turned ON instantly. |
| 15:39 | 71.1% | 13.89V | +34.4A | 5.2°C | ON | SUCCESS: Battery is warming up while charging. |
Analysis: The self-heating function worked perfectly. The moment a charge was applied to the 1.1°C battery, the BMS correctly diverted power to the 85W heater and began raising the battery's internal temperature, allowing it to safely accept a charge. The test was stopped at 5.2°C, but it is clear the heater was functioning as specified (it is expected to turn off >10°C).
Test 2: Deep Discharge (Cold) Data Log
Objective: To test the battery's performance under a high load from a cold state down to 0% SoC. Load: 950W Parabolic Heater (~92-100A draw).
| Time | SoC % | Volts (V) | Amps (A) | Temp (°C) | Heater Status | Warnings/User Notes |
|---|---|---|---|---|---|---|
| 15:49 | 74.6% | 12.82V | -92.0A | 9.2°C | Off | TEST START: Charge disconnected, heater ON. |
| 16:20 | 35.59% | --- | -96.1A | --- | Off | --- |
| 16:-- | 33.5% | 12.86V | -10.0A | 19.3°C | Off | (Heater off. Note: "LED, TV+Firestick, 12.86V stable") |
| 16:26 | 31.5% | 12.2V | -94.6A | 19.5°C | Off | CRITICAL FINDING: "Voltage drop to 12.19 causes electronics to turn off (TV+Firestick)" |
| 16:27 | 29.7% | 12.2V | -94.6A | 20.0°C | Off | Note: "12V TV will NOT turn on." "Remaining Time" estimate of 24m seems accurate. |
| 16:29 | 27.7% | 12.09V | -94.9A | 20.6°C | Off | "Battery Undervoltage Warning" Active. |
| 16:31 | 25.2% | 11.97V | -96.1A | 21.4°C | Off | Undervoltage warnings continue. |
| 16:35 | 20.2% | 11.78V | -96.6A | 23.3°C | Off | --- |
| 16:37 | 16.7% | 11.76V | -97.4A | 24.8°C | Off | Note: "Remaining Time" now shows 2h 12m (Highly inaccurate). |
| 16:43 | 9.7% | 11.23V | -100.5A | 28.3°C | Off | Cells: 2.82, 2.82, 2.81, 2.80 |
| 16:44 | 7.7% | 10.98V | -101.9A | 29.3°C | Off | Note: "KS2 inverter alarm because voltage dropped too low" |
| 16:45 | 0% | 11.24V | 0A | 30.2°C | Off | CRITICAL FINDING: BMS SHUTDOWN. (Last screenshot at 7.7% / 10.98V before final shutdown). |
| 16:46 | 0% | 12.38V | 0A | 30.4°C | Off | (Load removed, voltage rebounding) |
Test 3: Recovery from Deep Discharge
| Time | SoC % | Volts (V) | Amps (A) | Temp (°C) | Heater Status | Warnings/User Notes |
|---|---|---|---|---|---|---|
| 17:05 | 0.1% | 12.97V | +42.5A | 27.1°C | Off | CRITICAL FINDING: "Battery was fully 0% and not even Bluetooth worked. Now charging..." |
| 17:17 | 7.09% | --- | +44.0A | --- | Off | --- |
| 17:46 | 23.8% | 13.43V | +44.1A | 21.9°C | Off | --- |
| 17:50 | 24.2% | 13.27V | 0A | 21.2°C | Off | (Charge stopped to prep for next cold soak) |
Week 2 Key Findings & Analysis
- Critical Finding: Significant Voltage Sag Under Load. The most significant finding from this test is the battery's voltage performance under a standard, high-amp load. At a 31.5% SoC, a single 94.6A load (one 950W heater) caused the battery's voltage to drop from a stable 12.8V (at -10A) to 12.2V. This drop was severe enough to shut down other 12V-dependent electronics, including the trailer's TV and Firestick. This is a disappointing result, as one would expect the battery to maintain a more usable voltage (above 12.5V) while under a load that is well within its 150A continuous rating.
- Self-Heating Works Perfectly: The test at 15:27 provides 100% confirmation that the self-heating function operates as designed, turning on automatically when a charge is applied in sub-freezing temperatures.
- BMS Shutdown Sequence is Robust: The battery correctly protected itself at the end of the discharge test. The log shows a clear, safe shutdown sequence: 1) At 16:29 (27.7% SoC), "Battery Undervoltage" warnings appeared. 2) At 16:44 (7.7% SoC), the voltage dropped to 10.98V, triggering the inverter's low-voltage alarm. 3) At 16:45, the BMS performed a final, protective shutdown of the battery.
- Deep Discharge "Blackout": The finding at 17:05 that the battery's Bluetooth also shut down is critical. This means a user who fully depletes this battery cannot check its status and must apply a charge to "wake" the BMS. This is important information for any user.
- App "Remaining Time" is Unreliable: The "Remaining Time" calculation is a significant software flaw. It jumped from an accurate "24m" (at 16:27) to a wildly inaccurate "2h 12m" (at 16:37) while under an even higher load. This is misleading and should be reported to the app development team.
Graphing Analysis
- Charge Rate (with internal Heater): From 15:27 to 15:39 (12 minutes), the battery gained 5.8% SoC (65.3% to 71.1%). This is a rate of 0.48% per minute while the 85W battery self-heater was also on.
- Discharge Rate: From 15:49 to 16:45 (56 minutes), the battery drained 74.6% SoC(74.6% to 0%). This is a rate of -1.33% per minute under an average load of ~95A.
- Temperature Rise (Load): During the 56-minute discharge test, the battery's internal temperature rose from 9.2°C to 30.2°C (a 21°C increase) just from the internal resistance of discharging.
- Temperature Rise (Heater): During the 12-minute charge test, the battery's temperature rose from 1.1°C to 5.2°C (a 4.1°C increase) from the heater alone.
Week 2 Conclusion
This week's test successfully validated the battery's advanced cold-weather features. The self-heating function works perfectly. However, the deep discharge test revealed a significant real-world limitation: severe voltage sag.
The battery cannot maintain a stable 12V+ output for other electronics when under a high (but rated) load, causing system-wide issues. This, combined with the buggy "Remaining Time" in the app, are the two most critical pieces of feedback for this test cycle.
Renogy 120Ah Pro S1 - Week 2 Test Infographics
