Winter is Coming

I previously posted lead-acid battery voltage vs. temperature and state of charge (SOC). If you have switched to lithium iron phosphate, there is also a relationship between temperature, voltage, and state of charge. The drop is less, but remember that lithium cannot be charged below freezing and the battery management system (BMS) will disconnect the battery from charging below about 35F. Additionally, the BMS will disconnect the battery completely below 11.5 volts (typical setting) until charging current is applied and the battery rises above 11.8 volts (typical). I installed a Li-Time battery (weight savings, price, and the lead was dead) and I have experienced both sorts of cut-offs (very low slow solar through the winter, and charger failure). In both cases, the battery woke up when charging was applied.