Should you discharge a Li-ion battery all the way before plugging it in?

Is it especially pertinent when you get a new battery / laptop?

Should you keep draining it all the time, or leave it plugged in whenever you can?

All battery tips are welcome.

locked by Chris S Sep 20 '12 at 16:11

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  • TL;DR - NO, you should strive to keep Li-based batteries near "fully charged", and avoid discharge as much as possible (the deeper the discharge, the more they're "used up"). – Chris S Sep 20 '12 at 16:06

Li-Ion degrades with use, so you should prefer shallow discharges. I.e., always charge it as soon as possible. This is in contrast to Ni-Cd and Ni-Mh accumulators, which do like to be fully discharged from time to time to keep their full performance.

So normally you should plug in your laptop whenever possible.

Another thing that is bad for Li-Ion is heat, which unfortunately laptops produce. So ideally, you'd remove the accumulator if you don't need it, and store it half-charged in a cool place. But many laptops don't work well/at all w/o their accumulator, so that's more theory.

See e.g. http://www.batteryuniversity.com/parttwo-34.htm

The battery prefers a partial rather than a full discharge. Frequent full discharges should be avoided when possible. Instead, charge the battery more often or use a larger battery. There is no concern of memory when applying unscheduled charges.

Or Wikipedia: http://en.wikipedia.org/wiki/Lithium-ion_battery#Guidelines_for_prolonging_Li-ion_battery_life

Lithium-ion batteries should not be frequently fully discharged and recharged ("deep-cycled").

You may need to discharge it fully occasionally to recalibrate the capacitiy measuring electronics in the accumulator. Every 30 cycles or so should be enough.

  • Note that modern Battery Management Systems do not need to fully discharge Lithium based batteries, they simply measure the charge in a completely different way from older systems. – Chris S Sep 20 '12 at 16:11

"When possible avoid frequent full discharges. Instead, charge the battery more often. There is no concern of battery's memory when applying unscheduled charges. A high residual charge before recharge is a benefit rather than a disadvantage for chemistry of Li-Pol battery on all iPads. The best way is to keep battery between 40% and 80% charged. After LiP battery of iPad is charged to 80% capacity it switches to trickle charging with a potential to cause plating of metallic lithium, a condition that renders the cells unstable. One more incentive to keep battery of iPad between 40-80% is the rate of the charge loss when gadget is not in use. The charge loss amounts up to 6% per year when battery is fully charged, but only 2% per year when it is half-charged. Nevertheless, short discharges with following recharges do not secure the regularly calibration needed to synchronize the fuel gauge with the battery's state-of-charge. A deliberate full discharge and recharge every 30-40 charges fixes this problem." http://thehowto.wikidot.com/prolong-battery-lifespan-for-ipad


You should fully charge/ discharge your battery the first 3 times of use. Then, vary the charge cycles. So, charge it to 90% then let it drain to 15%; charge it 75% and then discharge to 20%. This has been proven by myself, and a lot of people I've suggested this to (including a school environment of over 400 laptops) work well.

Then discharge fully / charge fully only once every 20 cycles or so. And never leave it charging overnight - because this will cause 'overcharge' and eventually could fry the battery cells.

Good luck :)

  • I've never heard of this "varying the charge cycles" thing. Why does this help? Also, the warning about "overcharging" seems bogus. Li-Ion is always charged by a smart charger which will nmot overcharge. If you really overcharged it, you'd probably notice, because a Li-Ion cell will usually explode if sufficiently overcharged... – sleske Jun 30 '09 at 9:31
  • Because full charge / discharges aren't healthy for Li-Ion batteries. No, there is no 'memory' as was found in the earlier cadmium based batteries - by varying, as the quote says [quote]Frequent full discharges should be avoided when possible.[/quote] Theoretically, the 'smart charger' should not overcharge- and yet, i know plenty of people who leave their laptops plugged in and even with the 'smart chargers' have now got batteries that hold 10 minutes worth of charge. You can dispute the science, but my practical and personal experiences tells me otherwise. – oldSkool-Soldier Jun 30 '09 at 13:08
  • There are so many questions about batteries on SF now hopefully this will be the last one. oldSkool has a very valid point about leaving it overnight. Li-Ion batteries have a limited number of cycles they can go through, and leaving it in overnight performs a charge/discharge/charge/discharge/charge/discharge, effectively wearing the battery out without even using it. – Mark Henderson Jul 7 '09 at 2:39
  • @Farseeker: "leaving it in overnight performs a charge/discharge/charge/discharge/charge/discharge". I've never heard of it, and it seems unlikely to me. Any reference for that claim? – sleske Oct 12 '09 at 10:37
  • @Mark, that's really not how the whole "discharge/recharge" limited number of cycles works. – Chris S Sep 20 '12 at 16:05

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