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.
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.
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.
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).
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:
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.
If you have an extra battery that is used only once in a while:
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.
|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?
AND CPU performance is more important than battery life span?
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:
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...
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
See Panasonic ECO Mode web page for the details.
See Samsung web page for the details.
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.
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.
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.
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.
Many web sites recommend to disconnect battery when your laptop is AC powered because:
Although these are true, disconnecting battery may not be necessary for many cases and can even cause problems because:
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.
No. It is too cold for Li-Ion batteries and may cause permanent damage. Just cool room temperature is fine.
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:
This happens when the battery gauge overestimates the remaining capacity.
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.
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.
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.