Blog by Sumana Harihareswara, Changeset founder

19 Dec 2009, 18:54 p.m.

Everything I Knew (About Battery Care) Was Wrong

Hi, reader. I wrote this in 2009 and it's now more than five years old. So it may be very out of date; the world, and I, have changed a lot since I wrote it! I'm keeping this up for historical archive purposes, but the me of today may 100% disagree with what I said then. I rarely edit posts after publishing them, but if I do, I usually leave a note in italics to mark the edit and the reason. If this post is particularly offensive or breaches someone's privacy, please contact me.

Today I learned that I've been working from an obsolete understanding of how to keep my cellphone and laptop batteries from losing gobs of capacity over time. A simplistic summary follows for your benefit.

The batteries in my phone and my work laptop are lithium-ion batteries. Check yours -- the "Li-Ion" abbreviation means it's lithium-ion. As detailed sources explain, charging/discharging battery care for lithium ion batteries is the opposite of the conventional wisdom I had in my head, left over from the old days of nickel-based rechargeable batteries.

It used to be that you'd want to run batteries all the way down before starting to charge them again, because otherwise the capacity might get messed up. That's not true with lithium-ion batteries; it's recommended that you only rarely let an Li-Ion battery run down below 10% of its charge.

Lithium-ion batteries lose capacity, in the long run, if they sit overcharging a lot, or if they run hot a lot. So don't let them sit plugged into a charger all the time, and if you usually run your laptop plugged into AC power, think about removing the battery and setting it someplace cooler.

The moment a lithium-ion battery gets manufactured, it slowly starts losing capacity. So buying a primary battery + a spare battery simultaneously might be a worse decision than using a primary battery, then getting the spare battery years later, when your capacity has substantially degraded.

This came up because I assumed I should let my new N900 run down completely (on the partial battery charge from the factory) before plugging it in, and I was annoyed that plugging in the USB-to-microUSB cable to transfer files meant it was getting juice while the battery hadn't totally discharged. But I was wrong to worry! Thanks for straightening me out, Sjoerd.


Anne KG Murphy
19 Dec 2009, 23:39 p.m.

All good stuff to know, thanks!

(I was pretty sure the battery care process for laptop batteries was different, but didn't know what it actually was)

20 Dec 2009, 2:26 a.m.

You have an N900! Will you review it at some point?

20 Dec 2009, 19:29 p.m.

The problem starts when you have a phone like the G1 that regularly runs completely out of battery every day if you use it a lot.

29 Dec 2009, 1:03 a.m.

I, too, was living (mentally) in the dark ages. Okay, don't let it run down. Good for knowing.

29 Dec 2009, 15:49 p.m.

Thanks for the info!

29 Dec 2009, 21:45 p.m.

I'm glad this has been useful to people!

Brendan: I'm not sure whether I'll do a comprehensive review -- I will, however, be pointing people to useful Maemo apps and resources and so on as I learn. Today: how to use the Symbol key to type a pipe in the terminal.

Stormy: yeah, under those circumstances -- when even right out of the box the primary battery doesn't have enough capacity for everyday use -- it makes sense to just spend an additional USD20 and carry a spare battery from day one. That way the user can prevent the Li-Ion battery from emptying regularly, and of course keep the device available all day. You probably already know this; I'm just ruminating.