openinverter forum

This is my first winter with the car on the road in regular use. Unfortunately I still haven’t got around to wiring up the heated seat pads that live under the modules in my front battery box so I have no way to warm them, I was just wondering what peoples experience and advise is using the car in freezing or only a few degrees. I know to expect lower range and not to go demanding maximum power straight away, any other tips would be helpful

It is said everywhere that batteries don't like being charged in the cold as well. So I would be very much interested in the topic as well. I have used my batteries in the freezing cold a bit, range seemed lower but they worked. Was putting batteries in a warmer place for charging though just in case.

When it comes to LFP the effect is very pronounced. With NMC not so much. For example Nissan BMS still allows 70 kW charge power (almost 2C!) when the pack is 5°C - just seen yesterday. 70 kW is also the maximum.
The BMS limited discharge power to 110 kW instead of 125 kW at -2°C. Nissan do a cold wheather version with ridiculously small and weak heating pads that supposedly fire up at -20°C - so not relevant for anything south of Stockholm I'd think.

Range decrease comes from many factors:
- Increased air density of cold air (think intercooler turbo)
- Internal resistance and energy lost into heating the cell via the latter.
- Increased friction due to winter tires and wet road
- use of heater

Ok that’s quite useful info about how Nissan approach things, makes me less worried I’m going to damage them

Aside from all the things mentioned, I see significantly more voltage sag under power on a cold pack. One of these days Ill put a battery temp limit on throttle.

God idea

Whether or at what rate you can charge at a given temperature is dependent on the exact cell chemistry. Ideally you'll want to find the datasheet for your cells and then do whatever the datasheet says.

The next best thing is to find out what the original car does where the batteries were taken from.

I run Model S modules in up to -25°C, but have a heating system to heat them to 0°C before charging, because it's what the supposed datasheet says, and it's what Tesla apparently does. I also limit dc fast charging to 60A until the batteries have heated to 10°C. As for discharging, I use a dynamic system that limits power so that the cells never go below about 3.0V. This results in quite low power levels in -25°C, something like 20-30kW for the 12 module pack.

Keep in mind also that regen == fast charging. You need to limit it based on battery temperature, if your cells can't take it.