Two Victron 330ah Lithium batteries with heaters are installed (parallel 12 VDC) in our camper van. I ran a battery heater (BH) test. Overnight low was -11 ℃, battery 1 (B1) = 4 ℃, battery 2 (B2) = 1 ℃, and both had under temperature alarm A-SL22. The batteries were at 83% State of Charge (SoC). Turned the BH switch on. Drawing an additional 55 watts of power. Checked 2 hours later B1/B2 = 11 ℃; both in ready state. Turned on the generator for 30 minutes, 86% SoC. All good! Left the switch on. Overnight low = -11 ℃. Next day B1 = 12 ℃, B2 = 6 ℃; both in ready state. Short charging test AOK. Overnight low -6.7 ℃. B1 = 6 ℃, ready; B2 =4 ℃, A-SL22; 70% SoC. Later B2 = 5 ℃ still A-SL22. Overnight low 0 ℃. B1 = 7 ℃, ready, B2 = 5 ℃, A-SL22. Four hours later, B1 = 8 ℃, B2 = 6 ℃; both ready. Van temperature = 8.9 ℃. Batteries can be charged.
Questions:
At what temperature should the battery heater turn on?
At what temperature should the battery heater turn off?
How many watts should a battery heater draw when on?
Why aren't the battery heaters working?