One of the most common questions we get asked about lithium batteries is do they work in the cold? Today, we are going to answer this question and take a scientific look at lithium batteries and cold weather.
Table of contents
- What Are Lithium Batteries?
- Batteries and Chemistry
- The Cold Weather Lithium Myth?
- Lithium vs. Lead-Acid in the Cold
- My Thoughts On This Experiment
- What About Charging Lithium in the Cold?
- Our Personal Lithium Battery Cold Weather Experience
- The Best RV Battery For Cold Weather
What Are Lithium Batteries?
For starters, what are lithium batteries?
Lithium-ion based batteries use a lithium metal inside the battery to store energy for later use. Different lithium battery chemistries use different “ions,” but all are sort of lumped under this category.
Regardless of chemistry, these batteries are rechargeable and tend to have higher energy capacities compared to other types of batteries. Lithium batteries are becoming much more popular due to their energy capacity, allowing for smaller and lighter batteries. These batteries power many things, from tiny electronics to entire towns.
Lithium battery technology has taken a serious bite out of the traditional lead-acid battery market, particularly in the RV and marine space. This is due to the myriad of benefits they provide, including greater power density and low maintenance, just to name a few.
Batteries and Chemistry
Before we dive into the question of temperature performance and get technical with experimental stuff, let’s back up to some battery fundamentals.
The Oxford Dictionary states the definition of a battery as “a container consisting of one or more cells, in with chemical energy is converted into electricity and used as a source of power.”
Strictly speaking, ALL batteries you use are “electro-chemical”, meaning they have a chemical reaction going on inside them to produce or store electrons.
If we think of batteries as containing chemicals and reactions, then let’s now take one more step and talk about how temperature affects these reactions.
Chemical Reactions in Cold Temperatures
Temperature greatly affects chemical reactions. As temperature increases molecules move faster and possess more kinetic energy. When molecules collide, the kinetic energy of the molecules can break bonds, leading to chemical reactions.
If, however, the molecules are cold and moving slowly the chemical reaction will not occur as fast. The minimum energy requirement that must be met for a chemical reaction to occur is called the activation energy. More molecules possess this energy in warmer temperatures.
Temperature Effects on Batteries
Since chemical reactions slow down in cold weather, all battery types will suffer performance decreases in cold weather.
The reverse can be said in hot temperatures. The chemical reactions will increase and the battery may overperform. Because of this, high temperatures for prolonged periods can actually shorten battery life, as the chemical reactions occur faster.
But are different battery chemistries (lithium-ion vs. lead-acid, for example) subject to different temperature effects?
The Cold Weather Lithium Myth?
Many times we have heard people say “lithium batteries don’t work in the cold” without any scientific backing.
Where does this myth come from? Well, lithium batteries suffer from a phenomenon of lithium metal plating on the anode if charged at high rates in cold temperatures. This could cause an internal short of the battery and a failure. When you use lithium batteries, this limitation needs to be taken into account.
It does not mean the battery won’t work, however, just that it can’t charge.
Most commercially-available lithium battery packs have protections in place to prevent charging below a set temperature. This may be where this statement is coming from. Fortunately, a little bit of heating easily overcomes this challenge.
Lithium vs. Lead-Acid in the Cold
Truthfully, lithium-ion batteries work just fine in the cold. But how does their cold weather performance compare with their lead-acid rivals?
Battle Born Batteries, makers of lithium iron phosphate (LiFePO4) battery packs, performed a cold-weather test under laboratory conditions to find the answer.
They tested their batteries against a major lead-acid manufacturer to compare performance in a cold environment. The test involved setting up a bank of 2x 100AH Battle Born Lithium-ion batteries @ 12V and 2×100 AH AGM lead-acid batteries @12 V.
The batteries were placed in a freezer compartment and a series of tests discharging the batteries at rates of 30, 50, and 80 Amps were run. They repeated this test at four different temperature ranges:
- 67- 72° F
The team discharged the batteries to the low voltage cutoff recommended by the respective manufacturer.
The team chose the experiment’s discharge rates to better reflect how Peukert’s Law would impact performance as the temperature dropped.
Peukert’s law expresses the change in capacity of rechargeable lead–acid batteries at different rates of discharge. It basically says that the faster you discharge a battery, the less energy you will get out of it due to internal resistance and chemical losses. Lithium-ion batteries significantly outperform their lead-acid counterparts in this area when high discharge rates are needed.
While not completely unaffected, lithium batteries deliver back the energy put into them better when using large loads at any temperature. The results show this below:
After running 3 test per temperature range, the amp-hour capacity of the batteries was documented before the low voltage protection shut down the battery. The graphs above are the results of the first set of tests. Subsequent tests yielded similar results.
As the data shows, lithium-ion batteries work great in the cold compared to lead-acid. In their experiment, the Pukert effect was clearly visible as the accepted discharge power was significantly lower in the 80A discharge vs the 30A discharge on the lead acid batteries. It had much less effect on the lithium batteries even at room temperature.
As the temperature dropped, this effect became more noticeable. Once below freezing the lead acid battery was only able to produce 8.1% of its rated capacity while the lithium battery still produced 80% of its capacity.
If you want to see the experiement for yourself check out Battle Born’s Blog or download the paper below.
My Thoughts On This Experiment
Their experiment was well executed with good logging equipment and I am confident their numbers are accurate. The test shows that lithium will preform its task of discharging stored energy in cold weather exceptionally well.
One of the most interesting findings is how poorly the lead acid preformed even at room temperature. This was due to the Peukert effect as the rating for lead acid is usually using a very small draw over a 20hour period which is not how most people use the batteries.
They showcased the one drawback to lithium, however, when they could no longer charge when the batteries were in the teens.
I only have 2 critiques of the experiment:
#1 – Measure Energy, Not Power
The experiment measured Amp Hours from the battery which is a measurement of power. Power and Energy are not the same. Power measures the rate energy is moved, while energy is the ability to cause change or do work. Energy numbers would have been closely correlated and most likely would have learned even more in favor for the lithium batteries. Since voltage does not sag as much, it most likely would have produced even more energy.
#2 – Allow for recovery time of the lead acid
Lead acid batteries perform worse overall than lithium batteries, but they might be able to perform a bit better in a real world application than the experiment projected due to the recovery effect. Voltage is know to significantly recover in lead acid batteries after a strong discharge as the chemical reaction penetrates deeper into the battery.
I believe that if the discharge had been on and off over a longer period of time they would have performed marginally better and may have more accurately represented a real-world scenario. If a load were to be continuously applied, however, the situation set forth in the experiment would be accurate.
What About Charging Lithium in the Cold?
So, what do we do about not being able to charge the batteries in the cold? Its pretty easy, Don’t charge them in the cold!
You can use your cellphone when below freezing, but bring it inside to charge. The same goes for lithium packs: they need to be warmed before charging if they are located in places well below freezing.
Cold Weather Charging Protections
Electrical heating of the cells can accomplish this. Lithium batteries require a BMS (battery management system) that is a set of electronics that balance and protect the pack. This same BMS could easily trigger a warming circuit to use the charge energy to first warm the pack before charging starts.
Future battery packs will soon offer this for cold weather and many custom builds have already added it. I personally added this protection to a battery bank I built out of a Tesla Model S car battery that you can read about here.
Electric Cars already do this and is how they work in the cold weather. We drive a Chevy volt and it has a liquid cooled and heated circuit to keep the battery within its best operating limits. Teslas and many other cars do the same.
Battle Born Batteries even sells a heated wrap that can be used with any lithium battery when needed before charging.
Our Personal Lithium Battery Cold Weather Experience
We have been living off-grid with lithium batteries as our primary storage medium for 4 years now and have dealt with freezing temperatures multiple times. We make sure to keep the batteries in enclosed compartments at all times, even though the compartments were not heated.
One of the packs I built included electrical protections and used a heated pad that would kick on to warm the pack. The heated pad used the packs own power or solar energy. If the pack got too cold, temperature sensors would shut it off to protect if from charging. It was only a 40 watt heater, but it was more than enough to warm the small space to keep the battery within operating specs.
For the Go North expedition we installed the batteries in a non-heated compartment. Bleed heat from the adjacent heated space kept the temperature above 40 degrees, even if the temps were in the teens outside.
Both systems performed well. Like the experiment, we noticed very little to no degraded capacity from the batteries over a warmer day.
The Best RV Battery For Cold Weather
In conclusion, lithium batteries work great in the cold! Much better than their lead acid predecessors.
From Battle Born’s experiment, a basic chemical analysis, and our personal experience, we can definitively say that lithium batteries are the best RV battery for cold weather performance over their lead acid counterpart.
If you’re using lithium batteries in the cold, they will need to be heated before charging. Adding a heating circuit easily overcomes this drawback, and the benefits of using lithium batteries in the cold are significant over this additional effort. As for battery pack technology advances, we are sure we will see heated batteries as an option for needs in cold climates.
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