Should you fully discharge a Li-Ion battery on first use?

EvilHamster

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Jun 9, 2012
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Hi all. It says to fully charge and fully discharge a battery after first time use. And to do it 3 times.
https://uk.answers.acer.com/app/answers/detail/a_id/27666/~/preparing-the-battery-for-first-time-use

Does full discharge mean below 5%? Or is 20% enough. The reason I am asking is because from what I have heard, discharging a LI-Ion battery to below 20% is harmful to the battery. So should one still do it for the first time? (If it will only affect the accuracy of the readout a little, but leave the battery in better long-term condition, I think 20% would be preferable?)

Cheers.
 

As the battery is used, its voltage slowly drops. Calibration involves mapping the voltage to a % charge remaining. Correctly determining the % remaining requires actually using the battery for close to its full capacity. If the manufacturer says to discharge it to 10%, then I would discharge it to 10%. Stopping the calibration at 20% may result in the laptop reporting it has (say) 15% charge remaining in the future, then suddenly shutting off. Remember - until it's calibrated, the % remaining that it reports is just a guess. So "20%" may actually be 5%, or 30%, or could be 20%.

I'm a little baffled as to why you need to do it 3 times (2 times I can kinda understand, but 3 times?), but again I would defer to the manufacturer. They built it, they know how it works, they're the only ones in a position to say what's the best way to calibrate it.
 
Full discharge is usually to calibrate the battery monitoring software. If Acer is recommending 3 times, their software must need that many discharges to calibrate correctly. Yes it harms the battery a little, but without properly calibrating the battery, the % remaining won't be correct so you won't even know if you're getting close to empty in the future.

It says to discharge until the low battery warning appears. I believe Windows' default for that is 10%. Li-ion is typically good for about 300 charge cycles (from 100% to 0% back to 100%). So 3 cycles from 100% to 10% to 100% won't damage it appreciably.

Make sure you recharge the battery immediately after. An over-discharged Li-ion battery can catch fire or explode if recharged. So to prevent this, the charging circuitry will intentionally brick the battery (prevent you from ever recharging it) if it determines the charge level is too low. If you discharge the battery and leave it sitting, the gradual self-discharge can drop the battery's charge level past this threshold, resulting in a permanently bricked battery.
 

As the battery is used, its voltage slowly drops. Calibration involves mapping the voltage to a % charge remaining. Correctly determining the % remaining requires actually using the battery for close to its full capacity. If the manufacturer says to discharge it to 10%, then I would discharge it to 10%. Stopping the calibration at 20% may result in the laptop reporting it has (say) 15% charge remaining in the future, then suddenly shutting off. Remember - until it's calibrated, the % remaining that it reports is just a guess. So "20%" may actually be 5%, or 30%, or could be 20%.

I'm a little baffled as to why you need to do it 3 times (2 times I can kinda understand, but 3 times?), but again I would defer to the manufacturer. They built it, they know how it works, they're the only ones in a position to say what's the best way to calibrate it.
 

EvilHamster

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Jun 9, 2012
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I suppose you are right. Always a bit strange to do a full discharge on purpose. It's kinda like keying your brand new car. But as you said, in the long run, 3 discharges will not really matter anyway.

Cheers.
 
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