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01-07-2019

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best battery charge threshold

2019-01-07, 2:53 AM

It's great that Lenovo Vantage cares about the lifespan of our batteries and offers us a choice of charge threshold.  But it offers no guidance what maximum level to set, except that it should be less than 100%.  Lenovo must have studied the effect of maximum charge on battery lifespan, and I wish it would share that information with us.  Higher maximum offers a convenience for most users, but they might be willing to trade some of that convenience for some increase in battery lifespan.  We need data in order to decide. 

 

For example, does even setting the maximum at 95% have significant livespan advantage vs. setting maximum at 100%?  Without knowing such things we're just bumbling in setting battery charge threshold.

 

 

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3258 Posts

12-22-2008

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Re: best battery charge threshold

2019-01-07, 19:29 PM

I agree that "we're just bumbling in setting battery charge threshold" but I don't know how to be more precise than that because of all the variables involved.

 

A great reference for these sorts of topics is Battery University. In particular see BU-409: Charging Lithium-ion and How to Prolong Lithium-based Batteries - Battery University. These articles help to explain the issues and tradeoffs in recharging strategies.

 

In practice the thresholds you set not only affect battery life (number of cycles before the battery can no longer hold xx% of design charge) but also how long your particular system will run within those thresholds (which depends on the hardware, screen brightness, apps running, etc.)

 

I also find it useful to consider the battery as an expendible component. Generally it will last only a few years, typically 3 to 5 years. So I consider the price of a new battery divided by 3 to 5 as an approximate annual cost of owning a notebook computer.


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8 Posts

01-07-2019

DE

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Re: best battery charge threshold

2019-01-08, 0:00 AM

Thanks, Hausman for the excellent reference: How to Prolong Lithium-based Batteries - Battery University.  Its practical suggestion is:

 

A laptop battery could be prolonged by lowering the charge voltage

when connected to the AC grid. To make this feature user-friendly,

a device should feature a “Long Life” mode that keeps the battery at

4.05V/cell and offers a SoC of about 80 percent. One hour before

traveling, the user requests the “Full Capacity” mode to bring the

charge to 4.20V/cell.

 

I've had ThinkPads since the 600X and have "expended" very many li-ions.  But battery technology has improved while laptop build quality hasn't, so I'm semi-expecting my T480s battery to last as long as the T480s.  The battery is expensive and it's worth taking measures to prolong its life.

 

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11267 Posts

01-02-2010

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Re: best battery charge threshold

2019-01-08, 16:43 PM

I don't think there is one best answer for everyone and every situation.  Some charging circuits keep charging as long as they are plugged in.  Battery powered devices are used differently.  I have lots of battery-powered things, but I have 3 big ones I use very frequently.  I have a laptop and a cell phone that I charge, then unplug and use until the battery level gets very low.  I then charge those to 100%.  I have another laptop that I use like a workstation.  It is plugged into a dock and connected to A/C most of the time I am using it.  I start charging when it gets below 60% and I charge it to 85%.  My strategy may or may not work for you.


Rich


I do not respond to requests for private, one-on-one help. Your questions should be posted in the appropriate forum where they may help others as well.

If a response answers your question, please mark it as the accepted solution.

I am not an employee or agent of Lenovo.
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06-08-2019

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Re: best battery charge threshold

2019-06-08, 15:53 PM

Based on what was in the battery university link:

---

Most Li-ions charge to 4.20V/cell, and every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life. For example, a lithium-ion cell charged to 4.20V/cell typically delivers 300–500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600–1,000 cycles; 4.0V/cell should deliver 1,200–2,000 and 3.90V/cell should provide 2,400–4,000 cycles.

On the negative side, a lower peak charge voltage reduces the capacity the battery stores. As a simple guideline, every 70mV reduction in charge voltage lowers the overall capacity by 10 percent. Applying the peak charge voltage on a subsequent charge will restore the full capacity.

---


I take that to mean that if you want to get twice the number of cycles (600-1000 instead of 300-500), holding everything else the same (big assumption!), then:

 

Each 70mV reduces capacity by 10%, which means each mV reduces capacity by 0.142%  .  So if you want to reduce the voltage to 4.1V, that's 100mV less, which means you need to reduce capacity by 14.2%.  So if you set it to 86%, maybe you get twice the number of cycles.

 

Sounds like it's also very important not to let it stay too warm in general, so probably best to have your laptop some place with good airflow when plugged in.

 

These are just my interpretation of the articles above; I am not a battery scientist / chemist / etc.  :)

 

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