lead acid battery freezing point

Lead Acid Battery Freezing Point Temperature vs State Of Charge

Yes, A lead acid battery has a freezing point. It could become damaged or ruined. But under what circumstances will a flooded lead acid battery freeze (like those in your car or truck, tractor, riding mower, ATV, boat, generator, motorcycle, etc..)? I’ve included a lead acid battery freeze-temperature (versus state-of-charge) chart below…

Putting it simply, a completely depleted ‘dead’ lead acid battery will freeze at 32°F (0°C). When a lead acid battery is fully discharged, the electrolyte inside is more like water so it will freeze”.

What happens when your lead acid battery physically freezes? Likely, it will become irreparably ruined to a sufficient extent. The ice that forms will expand and press on the internal cells and plates (and bulging the wall/case of the battery itself). The case may even crack – resulting in leaks. Given internal physical tolerances, some (or all) of it may ‘short out’ inside. The battery may never hold a proper charge (or any charge) again.

However, a well charged lead acid battery in good condition will not freeze in practical use. But the less charged it is, the more susceptible to freeze damage. Even for a fully charged lead acid battery, there’s still a point of freezing. But those temperatures are extremely cold and you likely will not ever experience that cold (keep reading).

The problem arises when your battery is only partially charged. This is when you might run into trouble during the cold winter months.

A little more detail… The exact numbers vary a bit, depending on a few factors. A fully charged (lead acid) battery will freeze. But not until temperatures drop to -94°F (-70 °C)! That’s pretty much not going to happen anywhere here on earth, right?!

Can a flooded battery freeze?

The only way that a battery can freeze is if it is left in a state of partial or complete discharge. As the state of charge in a battery decreases, the electrolyte becomes more like water and the freezing temperature increases. The freezing temperature of the electrolyte in a fully charged battery is -92º F (-69º C). At a 40% state of charge, electrolyte will freeze if the temperature reaches approximately 16º F (-9º C).

~TrojanBattery

Important >> The less charge on the lead acid battery, the more susceptible it is to freezing.

I built a chart that cross references battery state-of-charge with the approximate temperature at which the battery will freeze. This is for lead acid type batteries. Car batteries, for example. Or those which typically install in lawn tractors, ATV’s, snowmobiles, maybe in your camper, etc..

Lead Acid Battery Freeze Chart
Temperature vs State of Charge

Lead acid battery freeze chart

The following article provides a better understanding of battery state of charge (approx.. corresponding open-circuit voltage). There are caveats to these measurements – which are clearly explained in the article:

[ Read: Battery State-Of-Charge Chart ]

As you can see, if your battery is only half charged (50% SOC), it could freeze solid at -4°F. This scenario is entirely plausible if you’re not careful. I often see temperatures below zero during the coldest winter months. The coldest I’ve experienced here was -32°F. It is not uncommon to experience early morning temperatures around 20 below at times throughout the winter here. So I need to be attentive.

I lost two 12-volt batteries several years ago in my 5th-wheel camper. Although they had been charged, I forgot to physically disconnect the batteries for the winter. As it turned out, there was a small parasitic drain constantly drawing down the batteries (propane gas detectors and a few other things). The batteries eventually went dead. And then they froze. It was an expensive mistake that I will never make again!

What about the 12 volt batteries on your tractor, lawn mowers, ATV’s, etc.. during winter?

Some people remove them and store inside where it’s warm during the winter. This is a good idea. Better safe than sorry, right?

However, you can leave a lead acid battery installed during the winter. But only if the battery is in good condition, there is no parasitic load slowly draining the battery, and the battery is fully charged.

To be sure, I periodically trickle charge my lead acid batteries with the following charger. This is the 12-volt Battery Trickle Charger that I have been using for years. Love it… Actually I have two of them.

Battery Tender Plus Trickle Charger
(amzn)

12 Comments

  1. Although I posted this a few years ago, when I woke up this morning it was 1 degree (F). It reminded me of this article, and it reminded me to give my outside batteries a renewed trickle charge today. I try to do it once a month during the winter months.

      1. Oh man, you should hear the noises the house makes when it’s down to 10 or 20 below or worse.. Expansion/Contraction is a real thing – yikes

  2. to be on the safe side i always take the battery off our lawn mower and store in garage till spring.

  3. I pull the batteries off of my camper and store them in the basement once the temps get low (right about now). They’re kept charged with rooftop solar panels, but use a cover in winter to keep the snow and ice off of them – so no sun, no battery charge.

  4. Thanks for the chart, very helpful. At 50 below, your car makes painful noises, the flat part on the bottom of the tires freeze, feels like driving on square tires, and power steering fluid has the consistency of toothpaste. You don’t get careless in weather like this.

    1. Sure thing about the ‘painful’ vehicle noises. When it gets real cold, I’ll plug in the truck engine heater (i’ve got a diesel). It zaps a lot of electricity, but at least the truck is a little happier on startup.

  5. At minus 20f, I needed to start the pickup out on the ranch. No electricity, had to go the hard way. Pulled the battery into the house to warm up. Drained the engine oil and antifreeze into pans (laying in the snow) and warmed them in the house on the stove. Replaced them all and started the truck. Half way to town, met the REA people repairing the line. Really really like having electricity. Yes, that old truck was a cold starting bitch, and doing just one of those items might have worked but experience won over laziness. The old beater did its job after you got it started.

    1. AJED,
      i can’t even imagine -20f. and yes, experience over laziness wins out every time.
      best of luck

    2. my grandmother used this trick to help many neighbors whose vehicles were parked outside in the winter in central Nebraska. Take an oil pan or feed pan and fill with charcoal briquettes. Light and when the fire is out and they are glowing, place under oil pan of vehicle. Wait. I don’t remember how long but when the oil was warmed the vehicles started every time. I think she was in her upper 80s outside after an ice storm helping a neighbor the last time she told about it. She wanted to help because he needed to get to work and she had a lot of respect for young people who worked hard.

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