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

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) rise in temperature cuts the life of a sealed lead acid battery in half. A VRLA battery for stationary applications that would last 10 years at 25°C (77°F) would only live for five years if operated at 33°C (92°F). The same battery would desist 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 over the past 10 years. In the 2000 study, a change of 7°C (12°F) affected battery life by roughly one year; in 2010 the heat tolerance has widened to 12°C (22°F). In 1962, a starter battery lasted 34 months, and in 2000 the life expectancy had increased to 41 months. In 2010, BCI reports an average age of 55 months of use. The cooler North attains 59 months and the warmer South 47 months.

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. Read more about Alternate Battery Systems. Figure 5 shows the drop in capacity after 700 micro cycles. The simulated start-stop test was performed in Cadex laboratories. CCA remains high.

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, and 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 get stressed if the equalizing charge is applied carelessly. 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. 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 turns 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 flooded systems, and the telecom industry switched 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.

A new lead acid battery should have an open circuit voltage of 2.125V/cell. At this time, the battery is fully charged. During buyer acceptance, the lead acid may drop to between 2.120V and 2.125V/cell. Shipping, dealer storage and installation will decrease the voltage further but the battery should never go much below 2.10V/cell. This would 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.  


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.