Advice on battery use


#1

Hello,

I read many many diverging advices on how to keep the battery longest.
Could you provide advice on daily use? Apart of the software tweaking possible. Is it better to let it discharge completely before to plug it in again? Or wait until its around 40% and charge it to 70%?

Thank you


Manually limiting battery charge
#2

Most important:

  • never discharge it completely (discharging a cell completely before charging is only useful for Nickel-Cadmium and, in some circumstances, for Nickel-Metal Hydride chemistries, but it's definitely harmful for Lithium-Ion batteries)
  • never keep it at high states of charge (say, above 60%) at high temperatures (above 50°C)

Less critical:

  • keep it cool, in general
  • don't charge it completely, stop when cells are at approximately 4.0V -- this battery has two cells in series, and you can check the pack voltage in sysfs, e.g.
    root@brigitte:~# cat /sys/class/power_supply/BAT0/voltage_now 
    7657000
    

    this is the pack voltage in µV. I guess the “smart battery” chip included in this battery actively balances the cells, so you can assume reasonably close voltages and just divide this number by 2 to get an estimation of a single cell voltage


  • charge it slower (I’m not sure if it’s doable with the Librem 13, but maybe limiting the input current at the DC jack could work)

  • before storage (if you were to buy a replacement, e.g.) charge it at 40% and then keep refrigerated (4°C). Check state of charge periodically (every 6 months), restore if necessary

The battery assembled in the Librem 13 is manufactured by Sunwoda in Shenzhen, model name is “TU131-TS63-74”. More information at: http://www.cvc.org.cn/swf/UN2014-0607-1.swf. You can also buy a replacement, see for instance http://www.aliexpress.com/item/New-and-original-The-Tablet-PC-battery-for-TU-TU131-TS63-74-7-4V-45Wh/32314737489.html. As it appears unlikely that Purism will offer any kind of support or replacements, I think I’ll buy one soon (as long as it’s still in production) and keep it in the fridge.

Sources: professional background. This guide: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries is also quite comprehensive.

Cheers
дядя Вова


#3

This is an amazingly instructive answer, thank you very much.


#4

Thanks Uncle Vova for the detailed info.

Battery replacement has been a concern for me since the beginning. I felt disappointed when Purism ignored (or forgot) my request to add a spare battery to my order.

I now have again some hope I’ll be able to get one.


#5

I don’t know how I missed this post, but this is fantastic information Uncle Vova!


#6

Why not charge completely? Everywhere else I read Li-Ion should always be fully charged.


#7

When overcharged (higher voltage) there’s a chance for micro short-circuit in lithium electrodes, which melts their fuzziness thus reduces their contact surface which in effect degenerates capacity. Again that supposed to be controlled by embedded protection circuit but you know, better safe than sorry.


#8

Is there battery charge control on Librem 13? Thinkpad used to have such functionality http://www.thinkwiki.org/wiki/Tp_smapi#Battery_charge_control_features


#9

A lot of folks that say to keep lithium ion fully charged are usually mis-informed on the different handling requirements of various battery chemistries, but some out there may be purposefully spreading mis-information to create additional demand for new devices. The reason I say this is: Take a look at the voltage of a fully charged laptop or cell phone battery. Chances are that the voltage at 100% charge is over 4.2 volts. I’ve seen my devices, both my XPS and Droid Turbo as high as 4.4 volts per cell, which is dangerously high and bordering on Thermal Runaway. Lithium ion batteries should never be higher than 4.2 volts per cell, and actually shouldn’t even stay at that voltage for very long if you want it to last more than a couple years. Since limiting the charge on my XPS to 74%, which is 4.0-4.1 volts per cell, battery degradation has stalled at 95.7% of design capacity, and this machine is going on 3 years old. It lasts just as long on a charge as the day it was new (actually better with TLP, so at least since I started using TLP tweaks).

General guidelines for lithium ion batteries are:

  1. Keep charge between 20-80% when possible. OK to go out of range occasionally, just keep it brief.
  2. Keep the battery cool. Temperatures above 85 F dramatically increase degradation.
    a. But not too cool. Do not charge when below freezing, as lithium plating can occur and permanently reduce capacity.
  3. Minimize physical stress. Do not charge a puffed pack. Discharge and replace.

Electric car batteries are usually the same chemistry as laptop batteries (the Tesla Model S and Model X actually using 18650 cells, just like older laptops), and their batteries last upwards of 10 years without significant degradation simply because they keep the batteries cooler and don’t go above 4.2 volts per cell, many only going to 4.1 volts at full charge. For this reason, I second the ability to adjust the charge profile, as this is a must-have feature for me to switch to a Librem from my XPS.