# What are some good practices for making sure my laptop battery serves its full life?

Basically, I'm looking for some do's and don'ts. Is it bad to keep my laptop plugged in when I'm not using it (majority of the time)? Is it bad to plug it in once I've finished using it (with it having something like 30% or 70% life left)?

This question comes up often and the answers are usually the same. This post is meant to provide a definitive, canonical answer for this problem. Feel free to edit the answer to add additional details.

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Good info here...h10025.www1.hp.com/ewfrf/wc/… –  Moab Oct 10 '10 at 23:11
Related question: Is it better to use a laptop on battery or on AC power? superuser.com/questions/12358/… –  sleske May 12 '11 at 10:24

I recommend doing the following to optimize battery life:

1. Keep my battery as cool as possible.
2. Don't worry about whether it's plugged in or not. When it doubt, keep it plugged in so it uses AC power instead of battery, unless of course it's getting hot.

It turns out that the two methods I originally posited are largely moot. The only thing that really matters is temperature.

"Temperature was the most significant factor contributing to the cell degradation, with state-of-charge (SOC) and discharge pulse length of secondary importance." (Liaw et al.)

Furthermore, it turns out that the decay can be accurately mathematically modeled:

Q = A exp(−Ea/RT) * t^z (See Ramadass et al. for explanation of terms)

However, the dominant model is that of the Arrhenius forumla, which generically predicts time-to-failure as a function of temperature.

The figure below shows the capacity at various cycle counts. Just look at the capacity on the x-axis. The top graph is at 25 C, the bottom at 50 C.

After 600 cycles, the cooler battery had ~2x the capacity

P. Ramadass et al. / Journal of Power Sources 123 (2003) 230-240

Fig. 7. Simulated discharge curves based on semi-empircal model for temperatures (a) 25 C and (b) 50 C. The dotted curves represent the experimental data obtained for Sony 18650 cells for the respective cycle numbers.

While I could still find no evidence on the behavior of Mac power circuitry, there was helpful information on the official Dell website. Two items specifically stood out.

Q. When docked or AC adapter is plugged into a wall outlet, am I using my battery charge?

A. No.

Q. Should I totally discharge, then recharge my Dell laptop battery occasionally to make it last longer?

However, it is important to note that Apple and Dell charging circuits may be different. Although, given that Dell does this, I assume Apple does as well. On this assumption, unless someone can provide sources to claim otherwise, I will assume that the Apple charging circuitry is smart enough to know this.

I encourage anyone to continue exploring this question and challenge my assumptions. Please see the sources below if you're curious for a more detailed explanation.

### Sources

1. Ramadass, P., Bala Haran, Ralph White, and Branko Popov. "Mathematical Modeling of the Capacity Fade of Li-ion Cells." Journal of Power Sources 123.2 (2003): 230-40. PDF

2. Liaw, B., R. Jungst, G. Nagasubramanian, H. Case, and D. Doughty. "Modeling Capacity Fade in Lithium-ion Cells." Journal of Power Sources 140.1 (2005): 157-61. PDF

3. Ning, G. "Capacity Fade Study of Lithium-ion Batteries Cycled at High Discharge Rates." Journal of Power Sources 117.1-2 (2003): 160-69. PDF

4. Ramadass, P., Bala Haran, Parthasarathy M. Gomadam, Ralph White, and Branko N. Popov. "Development of First Principles Capacity Fade Model for Li-Ion Cells." Journal of The Electrochemical Society 151.2 (2004): A196. PDF

5. Zhang, D., B. S. Haran, A. Durairajan, R. W. White, Y. Podrazhansky, and B. N. Popov. "Studies on Capacity Fade of Lithium-ion Batteries." Journal of Power Sources 91 (2000): 122-29. PDF

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Depends on your battery's chemistry, but assuming LiIon, most recommendations I've read have included:

• not running it all the way down (unlike NiCad chemistries that got "lazy" if they weren't run from full-charge to discharge).
• leaving it at ~ 40% charge if it will be out of use for long periods
• keeping it cool (e.g. remove i if you tend to mostly use the machine plugged-in).
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Laptop batteries' ideal life (from my experience) is around 2 to 2 1/2 years...I have a modern laptop around 2.5 years old, and the battery is already in questionable condition, even though it has been plugged in 90% of the time...Yes, it is true not to drain the battery completely, because it takes a charge cycle out of the life of the battery...

Honestly, if you are at your desk, and the battery is charged, I would recommend taking out the battery entirely. This way, you do not need to worry as much about it's life, at least in the long run.

Hope that helps!

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Modern lithium-ion batteries nearly don't suffer the memory effect. But you should not drain it completely till your laptop powers of because there is no energy any more. Hard to happen under Windows, but perhaps if your computer is stuck booting, or your OS is crashed. The main problem is heat. High temperatures increase the aging of batteries significantly.

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If you are on Windows, you can use this small free app to check your battery health in units for Designed Capacity, Full Capacity and Charged Capacity: HWMonitor.

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One thing you should do to help is about once every month, drain the battery completely and then recharge it completely.

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-1 because that advice is not true for all types of battery. –  Tim Long Oct 10 '10 at 18:14
Yeah; I know someone who killed a 9-cell Lithium Ion battery in a matter of months doing this. On my advice. D-: –  JamesGecko Oct 10 '10 at 19:00
It depends on the battery chemistry. That's true for NiCad, but bad for LiIon. –  JRobert Oct 10 '10 at 22:17
It should be noted that modern laptops practically always use LiIon batteries (or variants like Lithium-ion polmyer). I have never seen or heard of a laptop (less than 10 years old) that used anything else. –  sleske May 12 '11 at 10:26

Try to reduce the cycle count e.g. by not leaving the laptop in standby mode while running on battery.

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Try to connect to the wall when doing CPU-intensive tasks like installing updates, watching video, etc. This will reduce the wear on your battery, i.e. less charge-discharge cycles.

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