Laptop Battery Recharging

fmueller

Some years ago when my wife got her first laptop at work, the computer support people there told her she should be careful never to discharge the battery further than absolutely necessary. My wife has been anal about this, and I doubt her laptops have ever had less than 90% battery power.

The other day she got a new laptop - her third - and this time the computer support people told her it's important that laptop batteries are occasionally fully discharged. Apparently quite a few people at her work use their laptops like a desktop, ie they install the thing on their desk, plug it in and leave it in this position for several years until they are upgraded to a new computer. The support people are convinced that's damaging for the battery and possibly even the computer and blame a whole raft of problems on this practice.

To me all this sounds like variations to the good old rechargeable battery memory effect urban myths. Any other thoughts or speculations?

Frank

Snarkasm

They're not urban myths, really. In my experience, if you leave a laptop plugged in at all times, it'll kill the battery faster than it otherwise would have.

Note the distinction: laptop batteries will die on their own in time.

I try to take mine off of AC every once in a while and let it discharge, and I think that's the best policy. Use the laptop as it was intended - as a laptop, meaning it can be used portably - and you'll be fine.

The difference is usually that it'll die shorten its ability to hold charge in 2 years or 20 months instead of 3-4 years. Don't worry TOO much about it, but let it flex every once in a while.

Thrax

A li-ion laptop stored with a 100% charge in a 77°F room will lose 20% of its maximum capacity per year. Alternatively, a laptop stored in that same room with a 40% charge will only lose 4% of its maximum capacity. These states assume prolonged storage. If you're going to store a battery, discharge it to 40%, and put it in your refrigerator for best shelf life.

Li-ion batteries should never be completely discharged and recharged, however. This is called a deep cycle, and it's not (generally) good for lithium ion packs. The one exception to this rule: Every 30th charge, the battery should be fully discharged and recharged to calibrate the battery's internal electronics for its new lifetime.

TL;DR: While in regular service, the battery should be charged early and often. Don't fully discharge them. Store it at 40% charge in the fridge if you need to store it.

As for connecting it like a desktop: There's really no harm to this. Laptops come with extensive circuitry to ensure the safety and operation of li-ion batteries (they're actually quite dangerous without it). Once the battery is charged to nominal capacity, the circuitry stops the charge current. If anything, the batteries are dying early because they're just not being used, not because they're on AC power all the time.

ardichoke

Just make sure you let it come fully up to room temp after storing it in the fridge (read, sit at room temp at least overnight). Otherwise you risk getting condensation in your laptop which can obviously damage the circuitry.