How to extend laptop’s battery life span?

September 23, 2012 By | 9 Comments

In this article

This article discusses about how to maximize the life span of laptop batteries.

In this article, battery life span means the total number of cycles you can charge/discharge the battery before it looses significant amount of its capacity. On the other hand, battery life means the duration laptop can operate on battery with single battery charge. Please do not confuse between these two.

What you need to know about laptop battery

I do not want to make this article too technical, but I think it is very important to understand the fundamentals of battery technology. By understanding the fundamentals, I hope you will be able to evaluate the information on the Internet (unfortunately, there is a great deal of misinformation out there) properly. So bear with me for a moment.

Virtually all modern laptops use lithium-ion (Li-Ion) batteries and they have the following characteristics with regard to their life span.

  • They do not have so called “memory effect”
  • Battery ages in proportion to the amount of the energy stored to and taken out of it

    These two characteristics make repeating partial discharge (start re-charging before the battery completely drains or start discharging before the battery is fully charged) almost harmless for Li-Ion batteries.

    For example, performing two 50% discharge/charge cycles ages the battery same degree as one full discharge/charge cycle does.

    This means you do not need to (and should not) perform extra charge/discharge for the sake of battery life span extension.

  • High voltage on the battery accelerates the battery to degrade

    Charging the battery to 100% full state increases the voltage applied to the battery and this accelerates battery aging. Even if you stop charging or disconnect the battery after the battery is fully charged, the voltage remains high and accelerates aging.

    The best way to avoid this problem is to stop charging battery well before it become full. By stop charging at 80% of the battery capacity, you can almost double the number of charge/discharge cycle (but, please remember that you get 20% less battery life for each cycle).

  • Extreme temperature, both high and low, accelerates battery to degrade

    Especially the combination of high temperature and high voltage is harmful to the battery. It is important not to leave the battery in the direct sunlight or in a car where it gets hot or cold.

There are some more factors that affect battery life span, but as they rarely happen in normal laptop use, I will skip them in this article. If you are interested in the details, please refer to the links listed in the References section.

Another important factor you need to know about laptop (and many other Internet articles failed to mention) is:

  • AC adapter alone (without battery) may not be able to provide enough power for your laptop to run at high speed

    This depends on the capacity of your AC adapter and the design of your laptop, but if this is the case for your laptop, your laptop’s performance may be significantly limited when you disconnect battery.

What can you do to maximize battery life span?

- For your spare battery

If you have an extra battery that is used only once in a while:

  • Charge the battery to half way (40~50%), or if the battery is already charged above half way discharge to half way.
  • Disconnect the battery from the laptop and store it in cool (room temperature) place.
  • Top off the battery before you use it.

- For your primary battery

There is no single recommended charging method that works for everyone. Recommended method is determined based on several factors including your preference and your laptop’s design. You can find the charging method suitable for your situation by answering four questions and looking up the table below.

1. Best way to maximize battery life span
Does the battery gets hot when laptop is AC powered? [detail-2]
Is battery chage contoll program provided by the laptop manufacturer? [detail-1]
Is the battery detachable?
Does your laptop slow down when battery is detached? [detail-3]
AND CPU performance is more important than battery life span?
Recommendation
NoYesYes/NoYes/No
  • Use battery charge control program provided by the laptop manufacturer and set charge limit to 80% or lower
  • When necessary (when you need maximum battery life), raise the battery charge limit just before that
Yes/NoYesNo(N/A)
YesYes/NoYesNo
  • Charge battery to 80% (or less) and detach from laptop
  • Put the battery back only when you need it
  • When necessary (when you need maximum battery life), top off battery just before you use it
Yes/NoNoYesNo
YesYes/NoYesYes
  • Attach battery all the time
  • Charge battery to 100%
Yes/NoNoNo(N/A)
Yes/NoNoYesYes
2. Charge control: Lenovo ThinkPad
3. Charge control: Dell Latitude
4. Temperature reading: HP ProBook
5. Battery usage history
6. Conservative CPU control
7. Less conservative CPU control

Question details:

  1. Battery charge control program from laptop manufacturer

    Some laptop manufactures ship their laptops with a utility program that allows you to control battery charging process. Using such program, you can control battery charger to stop charging battery well below 100% while keep powering your laptop with AC power. This is very effective to avoid battery degradation caused high voltage.

    Some of the examples are:

    • Lenovo Power Manager (Figure 2)

      You can get to the battery charging mode control screen with the following steps.

      Control Panel > Lenovo – Power Controls > Switch to Advanced mode > Battery tab > Battery Maintenance…

    • Dell Battery Information (Figure 3)

      You can get to the battery charging mode control screen with the following steps.

      Start Menu > Dell > Feature Enhancement Pack > Power and Battery > Dell Battery Information > Battery Setting: Change Setting

    • Panasonic ECO Mode

      See Panasonic ECO Mode web page for the details.

    • Samsung Battery Life Extender

      See Samsung web page for the details.

  2. Measuring battery temperature

    Use your laptop with AC adapter and fully charged battery. Then run your typical workload for a while and check the battery temperature. Many laptops come with a vendor specific power saving or battery management program and you can read the temperature with it. (Figure 4)

    If no such program is available for your laptop, you can simply disconnect the battery (recommended to shut down or hibernate the operating system before that) and feel the temperature of all surfaces of the battery pack.

  3. Battery capacity you usually use during each battery mode operation

    Using Battery Life Maximizer, you can easily see how much battery capacity was remaining at the end of each battery operation. In the example shown in the right (Figure 5), you can see almost all battery operation ended with 20% or more remaining battery capacity.

  4. Does your laptop slow down without battery?

    It takes a little bit of work to find out the definitive answer for this question, but generally speaking, this happens when both of the following conditions are met.

    • Smaller (such as 65W or smaller) AC adapter is used

      You can find the capacity of your adapter in the label on it.

    • Your laptop is relatively new (released in the last couple of years)

    The screen shot on the left (Figure 7) shows an example of conservative CPU performance control. This was captured on a laptop with 2nd generation Core i5 CPU with 65W AC adapter. CPU performance is constantly limited to less than 40% of its maximum performance. You can easily feel the performance impact in this case.

    Another example (Figure 8) shows less conservative control. This was captured on another laptop 2nd generation Core i3 CPU with 90W AC adapter. In this example, CPU is allowed to run at 100% performance for some time, but occasionally limits the performance to less than 40%. You may or may not feel the performance impact in this case.

    If you want to check how disconnecting battery will affect your laptop performance for sure, please see the instruction in How to check if your laptop can run at full speed without battery section later in this article.

FAQ

1. Shall I disconnect battery when my laptop is AC powered?

Many web sites recommend to disconnect battery when your laptop is AC powered because:

  1. It protects the battery from high voltage (But this is true only if you disconnect the battery well before the battery is fully charged. If you disconnect after the battery is fully charged, you cannot get this benefit.), and
  2. It protects the battery from the heat generated by the laptop.

Although these are true, disconnecting battery may not be necessary for many cases and can even cause problems because:

  • As explained earlier, many laptop vendors provide utility programs that control the charge level. This will eliminate the problem #1.
  • In addition, batteries are often located at the cool part of the laptop such as the backside (near the LCD panel hinges) of the laptop. In these designs, battery temperature usually stays below 35℃ with normal use. If your laptop is designed this way, the problem #2 does not affect the life span of your battery.

On the other hand, many laptops are designed to limit its performance (limit the maximum CPU clock frequency) when the battery is disconnected. This is because the AC adapter alone may not be able to sustain the power needed by the laptop at its maximum performance state.

Some laptop lower the CPU clock only when its AC adapter cannot sustain the needed power (example in Figure 7), but some other laptop apply much more conservative policy and limit the CPU frequency to very low level while the laptop is powered by AC only (example in Figure 6).

If your laptop behaves this way, you may not want to disconnect battery so that you can get full performance of your laptop. You can check this by following the steps explained in How to check if your laptop can run at full speed without battery section in this article.

2. Shall I store unused battery in freezer?

No. It is too cold for Li-Ion batteries and may cause permanent damage. Just cool room temperature is fine.

3. Do I need to fully discharge battery periodically?

No. As mentioned at the beginning of this article, Li-Ion batteries do not have memory effect and do not require full discharge cycle to maintain its capacity.

If there is a reason to perform full discharge cycle, it is to re-calibrate battery gauge. After repetitive partial discharge cycles, battery gauge can be a little bit inaccurate. As a result, you may experience the problems like the following examples when you are using your laptop on battery:

  • Battery capacity seems to drop very quickly near the end of discharge cycle (for example, drop from ~20% to 10%)

    This happens when the battery gauge overestimates the remaining capacity.

  • Battery capacity stays almost constant for long time near the end of discharge cycle (for example, stays at 15% for an hour)

    This happens when the battery gauge underestimates the remaining capacity.

If you want to avoid these inconveniences, you may want to perform full discharge cycle, but you usually do not need to do it more than once in couple of months. If you do not care about the inaccuracy, or if you are repeating only shallow discharge, you do not need to do this at all.

How to check if your laptop can run at full speed without battery

8. Performance Monitor — Startup
9. Add Counter

This is a step-by-step instruction for Windows 7. The steps required for older operating systems are basically similar, but the details may be slightly different.

  1. Startup your laptop without battery.
  2. Open start menu and type Power Options into the search box to open Power Options control panel.
  3. Remember which power plan is currently selected (so that you can restore the setting later) and switch to Maximum Performance power plan.
  4. Close Power Options control panel.
  5. Open start menu and type Performance Monitor into the search box and start it.
  6. Performance Monitor starts up with CPU utilization (% Processor Time) graph (Figure 8).
  7. Press “X” button above the graph to remove the data.
  8. Press “+” button to open Add Counter dialog box.
  9. Expand Processor Information group in the right-top list box and select % of Maximum Frequency. (Figure 9)
  10. Select <All instances> in the right-bottom list box. (Figure 9)
  11. Press Add >> button.
  12. Make sure that the selected counter appears in the list box in the right and press OK button. (Figure 9)
  13. See how the numbers shows with some workloads. If the number is always 100%, it means your laptop can operate at 100% performance without battery.
  14. After you are finished, repeat step 2-3 and restore the original power plan setting.

References

Here are some web sites with useful and accurate information about Li-Ion batteries. If you would like to learn more about Li-Ion battery, these are good source of the information.

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Comments (9)

  1. Jason

    Regarding the flowchart: suppose the battery does not get hot while laptop is AC powered. What does that tell you, that leads you to opt for leaving the battery in the laptop instead of storing it?

    • Luculent Systems

      Hi Jason,

      I’m afraid, when I updated this article last time, I’ve oversimplified the logic and missed several important cases. Thank you for catching the flaw.

      I have corrected the mistake (and flow chart was replaced by a table).
      In your case (if battery does not get hot in AC mode), you still need to answer other questions to find out the optimal answer.

      Hope this will clear up the confusion.

  2. Prashant

    Do I need to disconnect the charger when battery is fully charged but I’m still using laptop?

    • Luculent Systems

      No. If you disconnect the charger, battery will start discharging.
      Keeping battery full is not a good thing for your battery, but repeating charging and discharging is worse.

      So, my recommendation is:
      1. If your laptop manufacturer provides a utility program that limits battery charge, use it to avoid full charge.
      2. If you don’t mind detaching the battery (or you know that you will not going to use the battery for long time), detach it BEFORE it is fully charged (or, if it is already full, discharge to 80% or lower before you detach).

      If neither works for you, just keep the AC adapter (charger) attached and keep your battery full charged. It’s still better than repeating discharge/charge cycles.

      Hope this helps.

  3. Malhar

    I have Lenovo G50-70 Laptop. My laptop use is 10-12 hours a day. if i take out the battery n use it, will it affect my battery?

    • Luculent Systems

      For battery life span, it’s always better to detach it (regardless how long/short you use your computer). It’s about how far you are willing to go for that benefit. As I explained in the article, your laptop may not give you full performance without battery. And, if the power cable is accidentally disconnected, your laptop will shutdown without proper OS shutdown process. This may cause problems. If you are willing to take those inconveniences and risks, please go ahead. Please don’t forget to detach your battery BEFORE it will be fully charged (ideally, at 80% or less charged). Otherwise, the benefit of detaching battery will diminish.

  4. ammu malar

    I bought a old acer’s lap to my bad luck it’s battery doesn’t have the capacity to run one hour, if I use internet it won’t run half an hour. What should I do now.

    • Luculent Systems

      I recommend to make sure that the battery has enough capacity. They can lose more than half of their capacity after couple of years of use. Please check “Full Charged Capacity” column in the Tools page of the Battery Life Maximizer. This number tells how much capacity your battery has. If this number is low, maybe you need to consider replacing your battery.

      The number mentioned above is based on the data from the battery, and some batteries (especially, cheap replacement batteries) report “too good to be true” numbers. To verify the accuracy of the number:
      1) Fully charge your battery and disconnect the charger.
      2) Keep your laptop as idle as you can until your battery (almost) empty.
      3) Go to “Battery Usage History” page of the Battery Life Maximizer and see the line of “Battery Capacity” decreased smoothly.
      If this line drops suddenly at some point, it’s a sign of degraded battery.

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