Lead Acid Batteries – State Of Charge versus Freezing Temperature

Yes, A frozen lead acid battery is a damaged or ruined lead acid battery. But under what circumstances will a lead acid battery freeze?

Putting it simply… A dead lead acid battery will freeze at 32 degrees-F.

However, a well or moderately charged battery will not freeze. (Sort of)

A little more detail… A fully charged (lead acid) battery will freeze. But not until temperatures drop to 94 below zero (-70 °C)! That’s pretty much not going to happen anywhere here on earth!

But >> Important >> The less charge on the 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, etc..

Chart: Lead Acid Battery – Approximate Freezing Temperature

As you can see, if your battery is only half charged, it could freeze solid at -4 degrees F.

Or, if it’s down to just 30% charge, the battery will freeze at 13 degrees F.

I lost two 12-volt batteries a few years ago in my 5th-wheel. I forgot to disconnect the batteries for the winter. As it turns out, there was a parasitic load constantly drawing down the batteries. Since I wasn’t charging them, they eventually went dead. And then they froze. It was an expensive mistake that I will never make again.

Since that time I installed a high current DC ON-OFF switch directly at the battery compartment location. I also make sure to FULLY CHARGE the batteries before winter sets in.

You can leave a lead acid battery installed and/or outside during the winter. But only if the battery is in good condition, there is no parasitic load, and the battery is fully charged.

This is the 12-volt Battery Trickle Charger that I have been using for years. Love it…

>> Battery Tender Plus Trickle Charger

I hope this helps some of you who may come across this post.

data sources include:
Math Encounters Blog – Battery Freezing Math

Here’s another short article that may help in the battery department:

[ Read: Battery State-Of-Charge Chart ]

Sort of related… One reason I chose AGM batteries for my off-grid solar power system was so I could keep them indoors. It gets very cold during the winters here. I knew that lead acid batteries can be a problem out in the cold (depending). And I knew that colder temperatures reduce the effective energy capacity in reserve. AGM’s are safe for indoors (no off-gassing of hydrogen). So that’s what I did.

Since then, Lithium battery technology has become popular. I might consider that option when my present battery bank reaches end-of-life.

For those interested in this, and the other choices for battery bank energy storage, I recommend that you check out IronEdison.com who specializes in this area:

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9 Comments

    1. Exactly! Thanks for pointing that out.
      It could also cause a crack and some or all the battery acid will leak out of that cell.

  1. I recently picked up a charger/maintainer with a desulfator mode. I have 3 different solar set ups. But only one has automatic equalization.
    I used it on a couple lawn mower batteries that I thought were near the end. It seems to have put some pep back in them.
    Also I use one of those small solar panel maintainers for the fifth wheel. It seems to be working well also.

    1. I use a battery maintainer on the quad and a 12v solar charger on the camper battery.
      Lawn mower battery gets pulled and sits in the basement.

      Batteries are not cheap. Treat them well.

  2. We’re supposed to have cold weather coming in a couple days. Depending how bad it is, I’m debating taking the battery out of my car so it doesn’t freeze. I can’t plug the car in, or drive it much at the moment which puts the battery at higher risk.

    1. You should not have to worry about it as long as your car battery is in normally good shape – and charged (which it should be because it gets charged while the car engine is running).

      On the other hand, if you know your battery isn’t much good anymore, well, yes you might have a problem in very cold temperatures as described above.

    2. YOLO:
      Depending on what you consider “cold weather” SoCa cold is 60 deg. Here cold is -5, Ken’s cold is -20 deg.
      As much as the battery, what temp Antifreeze is in the radiator?

      Something I have done when it gets really cold here, -20, I put a “drop light” under the hood. A 100 watt bulb puts out quite a bit of heat.
      BUT be careful, make sure you don’t burn the car down, make VERY sure the light is not touching ANYTHING that can catch fire.

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