Lithium Batteries & Cold Weather

Lithium Iron Phosphate (LiFePO4) batteries are an extremely popular choice for their high energy density, reduced weight, long cycle life, and excellent safety features. However, some special considerations are required if you plan to operate the batteries in an environment where they will reach temperatures at, or below, freezing (0°C / 32°F).

How does cold weather affect LiFePO4 batteries?

Like any battery, cold weather can cause a decrease in the overall performance. Chemical reactions within the battery slow down in low temperatures, leading to a reduction in capacity and power output. This can result in decreased run time and efficiency, especially in extreme cold conditions.  

Current LiFePO4 battery technology has a couple of hard limitations when it comes to cold weather use.  Most notably is that you can not charge a battery that is below 0°C without damaging it.  However, it is important to be aware of the distinction between ambient temperature (how cold the air is outside) and battery temperature (the actual temperature of the battery components/cells themselves).   

It is primarily battery temperature that we concern ourselves with.  Some simple steps like adding an insulated box around your battery can make a huge difference, and potentially eliminate cold weather concerns. 

Simple beverage cooler used for battery insulation (Sourced from Google)

 

What is the optimal temperature range for LiFePO4 batteries?

LiFePO4 batteries perform best within a temperature range of 10°C to 35°C (50°F to 95°F), however they are safe to use at a much wider range (-20°C to +50°C). Operating the batteries outside of this range can lead to potential damage, and reduced life expectancy. This is why it is important to have both high, and low, temperature protections in the batteries you buy.

Normal use of the batteries generates heat in the cells, electronics, and cables.  The more power you move in/out of the battery, the more heat is generated.  This is something we can easily leverage to our advantage.

What is Low Temperature Charging Cut-Off Protection?

Many batteries (but not all!) have a feature built in to prevent the battery from accepting a charge when it could damage the battery cells due to cold.   This is a feature of the Battery Management System (BMS) built in to these advanced batteries.   Using temperature sensors inside the battery case, the BMS monitors the internal component temperatures (and if it's Bluetooth enabled, so can you!), and if it moves below a certain point (often set at around  3°C), it will prevent the battery from charging.  

The battery remains functional for discharge (and powering your loads) but won't charge if a charger is connected to it.   This protective feature will turn off automatically, as soon as the battery warms up again.

How to optimize LiFePO4 battery performance in cold weather?

Obviously different installations will have different solutions, tailored to their particulars.  However, there are a few proven strategies to evaluate for your own setup.

1. Insulate the batteries: This is the simplest, and often most effective.  Use insulation materials to help retain heat and protect the batteries from extreme cold temperatures.   In a test I recently ran on my own batteries, I installed 1" thick polystyrene foam around the inside of the plywood/steel box I keep my batteries in.   I charged the batteries for a few hours in the evening, and their temperature reached 11°C (from ~4°C).   It was -11°C ambient overnight, with lots of wind, and my batteries were still +6°C in the morning.   For reference I average between 2 Amps & 7 Amps draw to run a fridge and a fan overnight (if you run heavier loads, your batteries will stay even warmer).

My Battery Insulation using 1" Rigid Building Insulation Foam

2. Preheat the batteries: If possible, preheat the batteries before using.  This is essential for charging, if your battery's internal temperature is near/below freezing.  This can be achieved by using a small heating pad (popular with the DIY crowd) on a timer/thermostat, or you can purchase self-heating batteries with this feature.  Of course, if your batteries are portable, the easiest is to just bring them inside!

3. Limit exposure to cold: Store the batteries in a warm environment  to prevent them from being exposed to cold temperatures.  This can be an insulated enclosure, or even just bring them inside.  They are safe to install inside your living area (no dangerous off gassing like lead batteries) and this ensures they stay near room temperature, giving you optimal performance.

4. Use a battery warmer: Consider using a battery warmer or heating pad to maintain the batteries at an optimal temperature during operation.  Some self heating batteries will keep themselves at optimal temperature by using battery power to warm themselves (some only heat during charging, so they don't drain your battery).   Be sure to check the specifications when purchasing a self-heating battery.

Special Instructions: Charging Below Zero Celsius

When charging LiFePO4 batteries in cold weather, it is important to follow the manufacturer's guidelines and recommendations. Charging below zero Celsius can be detrimental to the batteries and may lead to reduced efficiency and potential damage. If charging in cold temperatures is unavoidable, consider using a battery warmer or bringing the batteries to a warmer environment before charging.  

By taking some basic precautions, the use of LiFePO4 batteries in cold weather is easy. You can usually ensure their longevity and performance, even in seemingly challenging environmental conditions.

Ok.  What are "Self Heating" Batteries?

This is a battery configuration that includes a heating element inside the case, controlled by the BMS.   The idea is that the battery can help manage it's own temperature, to maximize it's efficiency and lifespan.  

This can be a very useful feature for anyone that expects their battery to reach temperatures near, or below, freezing when they need to charge it.  Perhaps you have a cabin with solar, or a camper trailer with a generator that you take out on weekends.   A self heating battery will make sure you can charge your battery when you need to.

It's important to note that there are a couple different approaches to a self heating battery, and you should check which kind you're getting when purchasing a battery.

Full Time Heating: Some batteries will self-heat anytime they drop below a certain temperature (let's say 10°C for example) and warm themselves back up using the battery's own stored power.  Often there is a limit so the battery won't heat below ~50% charge, to prevent killing the battery completely.  But be sure to check when buying.

Charging Heating:  These batteries only turn on the internal heating pad when you are trying to charge below temperature.  The BMS will block charging, but use the charger's energy to heat the battery.  Once safe charging temperatures are reached (often ~5°C), the BMS turns off the heater, turns charging back on, and the battery will start pulling power from your charging source.   Now the power flowing into the battery will help keep the battery temperature in the safe range.

In Conclusion

Cold weather is something to be aware of, but not scared of.  Unless your batteries are being installed remotely where it would be difficult to keep them above freezing temperatures, it's almost always just a simple matter of a a little insulation to keep them happy.

I always recommend that you purchase batteries with low temperature charging protections anyway, as this is the easiest way to protect your battery investment by automatically disabling charging when it could damage the battery.  This helps new users, and seasoned pros, alike.