I use a good-size Tesla battery-set, and (like the ones from the Mercedes) they have the water-cooling jackets built in.
I have mine plumbed in so that when driving the car the batteries are cooled as part of the water-cooling setup, but when charging the car and if ambient is below 50F the water-valves "flip" so I re-circulate the water only around the cells and then through an in-line water heater powered from the charging voltage.
The temp control is nothing fancy (Arduino w thermistors) for reading ambient and regulating the heater-power, but I can maintain 65F pretty easily (but this is Texas).
The heater-pads etc do work, but they typically run off of relatively high voltages. When they start to go bad they develop a "spot" heats up more than the rest, and it gets worse and worse until eventually that spot burns through (if there is enough power to be had). I would recommend some kind of monitoring circuit for off-normal currents.
I have mine plumbed in so that when driving the car the batteries are cooled as part of the water-cooling setup, but when charging the car and if ambient is below 50F the water-valves "flip" so I re-circulate the water only around the cells and then through an in-line water heater powered from the charging voltage.
The temp control is nothing fancy (Arduino w thermistors) for reading ambient and regulating the heater-power, but I can maintain 65F pretty easily (but this is Texas).
The heater-pads etc do work, but they typically run off of relatively high voltages. When they start to go bad they develop a "spot" heats up more than the rest, and it gets worse and worse until eventually that spot burns through (if there is enough power to be had). I would recommend some kind of monitoring circuit for off-normal currents.
