Lithium ion question

Edward Yee · Post by **Edward Yee** » 2007-10-25 11:40am

What's better for (laptop) battery life, recharging frequently or longer, above-3% discharges? Is there any "sweet spot" for battery life?

That is, better to recharge a battery at say 98% (2% discharge before recharging, say if I go from a classroom to a lounge) or say wait til 40% or even 5% (before it can hibernate)? Which tendency would better preserve/draw out storage capacity?

Seggybop · Post by **Seggybop** » 2007-10-25 02:10pm

I may be confused, but if I recall correctly they last the longest if they never get below 45% and that waiting until they're almost dead and then recharging them is the worst. Also, they degrade in capacity to some degree as they age regardless of whether they're being used or not, with the degradation rate dependent on the temperature.

aerius · Post by **aerius** » 2007-10-25 02:31pm

General consensus is that frequent top-up charges are best, and full discharges are to be avoided. A full discharge for every 30 or so charge cycles is recommended to keep the battery's fuel guage & protection circuitry calibrated.

Edward Yee · Post by **Edward Yee** » 2007-10-25 03:46pm

Is it better to charge to 100% each time, or partial charges okay?

Starglider · Post by **Starglider** » 2007-10-25 06:18pm

Edward Yee wrote:Is it better to charge to 100% each time, or partial charges okay?

Unlike ni-cad (or even nimh) usage cycle doesn't make that much difference for lithium-ion batteries. The control circuitry generally prevents you from taking the voltage low enough to damage it. Leaving batteries sitting completely discharged for long periods is a bad idea (because the self-discharge rate will take the voltage down to levels that start to shorten the battery life).

However the single biggest thing that shortens lithium battery life is high temperatures. For laptops, taking it out of the laptop when you're using it on mains power can make a considerable difference, as can those cooling pads you can get. Leaving anything with a lithium battery in it inside a hot car for long periods is a bad idea.

Hawkwings · Post by **Hawkwings** » 2007-10-25 09:05pm

don't Li-ion batteries completely die if they go down to 0 charge, and you can't recharge them anymore?

SCRawl · Post by **SCRawl** » 2007-10-25 10:32pm

Here's another question: if a Lithium-ion-powered device is "plugged in" while being used, is the battery being used at all? Do any of the charge cycles get "used up"?

aerius · Post by **aerius** » 2007-10-25 11:03pm

Hawkwings wrote:don't Li-ion batteries completely die if they go down to 0 charge, and you can't recharge them anymore?

Yes. However most Li-ion batteries have a built in protection circuit which shuts off the power before the battery gets drained down to zero.

SCRawl wrote:Here's another question: if a Lithium-ion-powered device is "plugged in" while being used, is the battery being used at all? Do any of the charge cycles get "used up"?

Depends on the design of the device & its charging circuit. Some devices will automatically charge the battery until it's full while plugged in, others will take the battery out of the circuit and run off the power from the wall. You'll have to hunt though the service & tech manuals to find out what each device actually does, and in many cases you'll probably never know for sure.