BU-806a: How Heat and Loading affect Battery Life

Learn about the temperature and how start-stop shortens the life of a starter battery.

Heat is a killer of all batteries and high temperatures cannot always be avoided. This is the case with a battery inside a laptop, a starter battery under the hood of a car and stationary batteries in a tin shelter under the hot sun. As a guideline, each 8°C (15°F) raise in temperature cuts the life of a sealed lead acid battery in half. A VRLA battery for stationary applications that will last 10 years at 25°C (77°F) would only live five years if operated at 33°C (92°F). The same battery would cease after 2½ years if kept at a constant desert temperature of 41°C (106°F). Once the battery is damaged by heat, the capacity cannot be restored.

The life of a battery also depends on the activity and is shortened if the battery is stressed with frequent discharge. According to the 2010 BCI Failure Mode Study, starter batteries have become more heat-resistant. In the 2000 study, a temperature raise of 7°C (12°F) affected battery life by roughly one year; in 2010 the heat tolerance has been widened to 12°C (22°F). Other statistics reveal that in 1962, a starter battery lasted 34 months; in 2000 the life expectancy had been increased to 41 months. In 2010, BCI reports an average age of 55 months cranking vehicle engines of which the cooler North attains 59 months and the warmer South 47 months. Colloquial evidence in 2015 reveals that a battery kept in the trunk of a car lasts one year longer than if positioned in the hot engine compartment. 

Cranking the engine poses minimal stress on a starter battery. This changes in a start-stop function of a micro hybrid. The micro hybrid turns the IC engine off at a red traffic light and restarts it when the traffic flows. This results in about 2,000 micro cycles per year. Data obtained from car manufacturers show a capacity drop to about 60 percent after two years of use in this configuration. To solve the problem, automakers are using specialty AGM and other variations that are more robust than the regular lead acid. [BU-211, Alternate Battery Systems]

Figure 1 shows a capacity drop from 100 percent to about 50 percent after the battery had been exposed to 700 micro cycles. The simulated start-stop test was performed in Cadex laboratories. CCA remains high and only shows a decline after about 2,000 cycles.

Capacity drop of a flooded starter battery when micro cycling

Figure 1:
Capacity drop of a flooded starter battery when micro cycling

Start-stop function
on a micro hybrid stresses the battery; the capacity drops to about 50 percent after two years of use. AGM is more robust for this application.

Courtesy of Cadex, 2010

Test method:   The test battery was fully charged and then discharged to 70 percent to resemble the SoC of a micro hybrid in real life. The battery was then discharged at 25A for 40 seconds to simulate engine off condition at stoplight with the headlight on, before cranking the engine at 400A and recharging. The CCA readings were taken with the Spectro CA-12.

The cell voltages on a battery string must be similar, and this is especially important for higher-voltage VRLA batteries. With time, individual cells fall out of line; applying an equalizing charge every six months or so should theoretically bring the cells back to similar voltage levels. While equalizing will boost the needy cells, the healthy cell gets stressed if the equalizing charge is applied carelessly. (See BU-404: Equalizing Charge)

What makes this service so difficult is the inability to accurately measure the condition of each cell and provide the right dose of remedy. Gel and AGM batteries have lower overcharge acceptance than the flooded version and different equalizing conditions apply. Deteriorating cell balance is related to aging and any attempt to re-balance will not correct the condition but provide a Band Aid solution to extend battery life. Always refer to the manufacturer’s specifications.

Water permeation, or loss of electrolyte, is a concern with sealed lead acid batteries, and overcharging contributes to this condition. While flooded systems accept water, a fill-up is not possible with VRLA. Adding water has been tried, but this does not offer a reliable fix. Experimenting with watering will turn the VRLA into unreliable battery that needs high maintenance.

Flooded lead acid batteries are one of the most reliable systems. With good maintenance these batteries last up to 20 years. The disadvantages are the need for watering and providing good ventilation.

When VRLA was introduced in the 1980s, manufacturers claimed similar life expectancy to the flooded systems, and the telecom industry was enticed to switch to these maintenance-free batteries. By mid-1990 it became apparent that the life for VRLA did not replicate that of a flooded type; the useful service life was limited to only 5–10 years. It was furthermore noticed that exposing the batteries to temperatures above 40°C (104°F) could cause a thermal runaway condition due to dry-out condition.

A new lead acid battery should have an open circuit voltage of 2.125V/cell. This indicates a fully charged battery. During buyer acceptance, the lead acid may drop to 2.120V. Shipping, dealer storage and installation will decrease the voltage further in idle mode, but the battery should never go much below 2.10V/cell as this could cause sulfation. Battery type, applying a charge or discharge within 24 hours before taking a voltage measurement, as well as temperature will affect the voltage reading. A lower temperature lowers the OCV; warm ambient raises it.

Last updated 2015-04-29

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On December 3, 2011 at 9:24am
Christian Pérez Ortiz wrote:

Hi, i find this article very useful, but yet i have a few questions:
I understand heat and frequent discharges can shorten battery’s life, so if I’m using my laptop (with a 6-cell Li-ion battery) as a desktop, I should take out the battery and work with electric current directly, right? I mean, if i wanted to avoid damaging my battery.

On December 9, 2011 at 1:49pm
Guillaume wrote:

Hi Christian,

you got it right. To maximize your laptop battery life expectancy, you should remove it from the laptop when you are connected on the sector (direct electric current). I would also add that you should make a partial discharge of the battery before removing it from your laptop.

If my memory serves me right, the optimal capacity for a laptop battery storage is 40% of the maximum capacity. You could confirm this information by doing a quick search on our friend google.

I hope I answer your question.

On December 9, 2011 at 1:55pm
Guillaume wrote:

Just made a quick search and found that on this website:


As you can see, I was on the track with my 40%. Note that a lower storage temperature is better.

On December 9, 2011 at 1:57pm
Guillaume wrote:

Check this link:


As you can see, I was on track with my 40%. Note that a lower temperature storage is better to save your battery life.

On December 9, 2011 at 10:32pm
Christian Pérez Ortiz wrote:

Thanks Guilliaume, so i will have my battery at a 40%. I’ll keep reading about this =D.

On December 12, 2011 at 6:41am
Guillaume wrote:


My pleasure. If only I knew that before wasting my own laptop battery.

P.S : Sry for double posting.

On February 18, 2012 at 7:43pm
Tom wrote:

Hi, can you please tell me the best way to store spare AW IMR18650 3.7v 1600mAh Battery’s.  l have a few spare bettery’s that l wont be using for a while and have been told that l should put them in the fridge, l don’t know if this is right but that’s what l have done.
Also can you tell me how long these new spare battery will last stored before they become useless.
Your answer would be much appreciated.

On February 20, 2012 at 2:09pm
Guillaume wrote:


The fridge is an excellent solution to store your extra batteries on the long run. Keep them in their original box if possible. If these batteries are Li-Ion, be sure to store them at 40% capacity.

On September 10, 2012 at 7:39pm
Mary Jensen wrote:

I have a clock that is mounted a brick wall outside that faces south.  It does get very hot in the afternoon. The clock does not keep up with the current time. What kind of battery can I use (AA) so the heat does not affect the time.

On October 18, 2013 at 5:19am
Ed Maltby wrote:

I am looking into the best solution in battery type and battery management for a fleet of transport truck, we currently use the AGM deep cycle but results are not as great as we hoped. We currently use 7 battery , 4 for truck starting and the other 3 to mantain air contioning for the cab when truck is shut off. Is there a better solution.


On January 30, 2014 at 1:46am
John Fetter wrote:

Mary - Move the clock. It is not the battery but the quartz crystal oscillator that drives the clock mechanism that does not like the heat. Quartz is not normally sensitive to heat but competition forces down prices and quality.

Ed - You need to find a way of giving the batteries a voltage boost from time to time with an old fashioned transformer-rectifier charger. The on-charge, fully-charged voltage must reach 15.5 for a 12 volt battery. After that switch off. Once every +/- three months.

On March 4, 2014 at 4:31pm
Siddharth wrote:

I need to know the author of this arcticles’ full name. I need to know for a referance list for the Regionals Science Fair.

On March 9, 2014 at 11:51am
Abdulwasey wrote:

Please advise me on the type of batteries that can be used in arid regions where the daytime temperature reaches 55-60 deg Centigrade to power the streetlights using Solar panels.
Best reagrds

On April 17, 2014 at 1:11pm
Enrico Stanzani wrote:

Very satisfactory informative paper

On April 17, 2014 at 2:29pm
John Fetter wrote:

Use regular batteries. Instal them underground.

On August 25, 2014 at 2:17am
Peter Smith wrote:

I have AGM batteries in a motorhome. They are charged off solar panels via MTTP regulators. Also from the engine when running.  Do your comments about a 3 monthly charge with transformer/rectifier unit apply to this setup? Thanks

On August 25, 2014 at 2:38am
John Fetter wrote:

Peter - Once every three months, overnight, using transformer/rectifier unit, definitely yes.

On October 10, 2014 at 10:22am
Sobin Tep wrote:

I have a question for any who can answer.

I have a device which is running on two AA Duracell batteries. The batteries (brand new) together is producing 3.4 volts (1.62 volts individually), which is estimated to run at least 2 years.

I am wondering if “temperature” (Heat, Cold, Humidity) plays a part in reducing the life span of the batteries?

The device does not consume much volts to shorten battery life span, so i am wondering if temperature is a crucial factor.

On November 30, 2014 at 4:48pm
A_Random_Guy wrote:

i also need the author’s name so if anyone can tell me in 1 hour i would like to know. This is very unlikely i will get an answer but i’m trying.

On November 30, 2014 at 4:51pm
Another_Random_Guy wrote:

i also need this for science fair. this website was really useful. I am not the same random guy. wink
BTW i hope you all had a wonderful thanksgiving!!!

On December 21, 2014 at 7:34pm
sidk wrote:

Hello all,
I am designing a battery charger for Panasonic LC-R064R5P and want to know battery health by monitoring temperature. Can anyone please tell me what will be the temperature of a battery if charged after its lifetime?
Waiting for some clue and suggestions, Thanks all.

On January 23, 2015 at 8:25am
Aaron wrote:

I work in the fireplace industry.  We use AA’s and D type batteries for either the receiver for a wireless remote or a a backup for fireplaces using an IPI system.  These batteries are installed and kept in close proximity to the firebox.  Though the area they are installed in generally will not reach higher temperatures than 120°F, the area is a good example of “not idea” when it come to battery placement for storage or use.

My question is: does one type of battery technology (available in AA’s and D’s) have a higher durability in this kind of environment?

On January 30, 2015 at 7:05am
Ismail wrote:

Is there a way to store Deep cycle lead acid batteries in enclosures that protects batteries from getting too hot/cold ?

On February 26, 2015 at 12:58pm
Cam wrote:

Is it possible to charge a 6volt (qty 6)  batteries to often.Have 6 in a golf cart, and it is only good for about 40 mins of use. Batteries are 3 yr’s old, on an automatic charger that shuts off with Batteries charged.Batteries are the Trojan brand.Can this problem be corrected?

On June 8, 2015 at 8:08pm
carl wrote:

if a lower temp causes a lower ocv does that mean sulfation ocurs more at a lower temp?

On June 8, 2015 at 11:23pm
John Fetter wrote:

carl - Sulfation occurs when the owner of the battery does not charge the battery properly. If you store a battery in the fridge it will be barely sulfated after a year. Store it at room temperature in summer and it will be fully sulfated. None of this has anything to do with oc voltage.

On July 23, 2015 at 5:41pm
Jay wrote:

Hello. So I’m trying to figure a couple of things out for a project. I would like to know how hot can a regular standard AA battery get as well as C D volt batteries. And can I increase the heat by adding more batteries? But if they reach a certain temperature what can I do to keep them cool during use? Transfering hear from the batteries to something titanium will it be just as hot if not what can I do to do so.

On July 26, 2015 at 10:11pm
Richard Phillips wrote:

I have a small RE system with 4 x L16 6V batteries in series to make 24V 430Ah. My first set of batteries lasted only 2 years I believe due to excess heat. My controller logs max/ min battery temp and shows the batteries over 40 deg C regularly when absorption and EQ charges were applied.
So, with this new set of L16 I have purchased a chest freezer and put the batteries inside with the lid open a little and filled with water 2/3 rds up the batteries. I have a separate controller to monitor the water temp inside and have set it to cut power to freezer at 20 deg C. It is now mid-summer here in Portugal and so far the batteries have not gone above 28 deg C even during EQ charge. I hope this set will last longer by keeping temperatures around 25 deg C I could lower even more perhaps down to 15 but this will use more energy to keep it there as ambient here is 25 at night and 40 in the day so 20 seems a good compromise.
I hope this idea helps someone else I also hope to get much longer from battery set this time

On July 26, 2015 at 11:31pm
John Fetter wrote:

Richard - If your L16 batteries lasted only 2 years and the battery operating temperature regularly went over 40 deg C, it seems highly unlikely that temperature alone caused the batteries to fail. I have worked with many tens of thousands of industrial batteries and it is quite normal for these batteries to go over 40 deg C. Industrial batteries are cycled from 100% down to 20%  and back up to 100% 200-300 times a year and usually last 5 to 8 years.
It appears from your comments that you have not run your “deep-freeze” batteries for long enough to support your claim. I am not trying to suggest that your idea is not a good one. You are recommending an untested procedure.

On July 27, 2015 at 2:48am
Richard Phillips wrote:

John - Thank you for your comments you are right, the procedure is untested for me only had the new set of L-16’s two months. I thought perhaps by posting this idea someone else may be able to chip in with better experience on cooling the batteries.
Looking at the technical sheet for these L16’s the graph curve shows approx 750 cycles for 80% dod which, when cycled every day as I do, is around the 2 year mark. My only problem with that is I have a Smartgauge monitor which switches the inverter relay back to mains at 50% dod so they have never gone below half empty assuming the monitor is working correctly. The same graph shows approx 1200 cycles at this discharge level which is over 3 years hence my assumption the excess heat may have caused the problem. Time will tell my setup is identical except for the addition of cooling the batteries I hope to be posting back in 8 years with good news.

On July 27, 2015 at 6:07am
John Fetter wrote:

Richard - Your “deep-freeze” method uses power. There is a “free” source of cooling below our feet. Go down into the ground and you find a rather pleasant ambient temperature, which a town in Australia has been using for many years. People in this town have actually buried their homes in order to keep cool. You might like to think of some kind of water tank buried underground, the batteries in contact with the water. The reason why I am suggesting a water tank is so that you achieve maximum contact area.
I visited a US military installation in the middle of a California desert in 1998, where they were running a big solar installation. The battery room was cooled by air-conditioning run from the batteries.

On July 27, 2015 at 7:54am
Richard Phillips wrote:

John - Another solid idea unfortunately I live on a hill with 20cm of topsoil and solid rock below that it would take a machine with a breaker many hours to make a hole big enough…  a stick of dynamite may do the same job but either way beyond my budget i’m afraid. 

The freezer draws 90W or about 4A from my 24V system which produces 60A all day when full sun. If you think about it the cooling is only really required when really hot & sunny at which point there is plenty of energy to go round so is a compromise for my situation. I did try the freezer without the water to start with but the batteries soon got hot during charging so put the water in to give a larger cooling capacity and so far it works well.
It’s 4pm in the afternoon here ambient outside in the shade is 44 deg C and my batteries are showing 100% charged and a steady 26.

On August 12, 2015 at 2:19am
Wong Enoch wrote:

Can a deep cycle battery be damaged barely two months because of high temperature

On August 12, 2015 at 3:07am
Wong Enoch wrote:

What is the best temperature can a 24v deep cycle battery be run

On August 16, 2015 at 6:19am
Stephanie Barnard wrote:

This is a great article full of great information. I was reading through some of the comments and questions and noticed some people asking about the affects of temperature on batteries. I also was curious about this topic. I recently wrote an article about the affects of heat on batteries and how to prevent battery failure. I hope it helps:  http://vatire.com/support/1294/how-are-car-batteries-impacted-by-summer-heat/

On September 16, 2015 at 8:00pm
Paul wrote:

Hi, thanks for this website, its fascinating, i have a challenge with the inverter i design my self once the battery runs down the battery dies automatically, what do i do to protect this battery, its causing problem between me and my customer.

On September 16, 2015 at 11:23pm
John Fetter wrote:

Paul - It appears you forgot to include a battery undervoltage detector in your design. Assuming a 12 volt battery, you need to set the detector to 10.5 volts. Once triggered, the inverter must be kept off by this circuit until the charger has had a chance to put something into the battery and the battery voltage has risen to above approximately 13.5 volts.