Re: Question on lithium ion batteries.

over discharging will cause damage
over charging will also cause damage (but less so)


If the laptop is going to sit on your desk plugged into power for 90% of 
its life, run the battery down a bit (like to 50% charge), then turn the 
laptop off and take the battery out (assuming you want it to last when 
you go on the road), Once every few months, charge it up, run it down to 
about 20%, charge it again, then run it back down to 50% and take it 
out. Leaving the thing on charge all the time will generally kill it.

The more you discharge the battery the less lifespan it will have, so if 
you can charge it at 50% all the time (assuming you are a regular user 
of said battery) it'll last longer than if you discharge it to flat 
every time. I reckon with modern batteries 30% charge is probably a good 
cutoff point in terms of cycle life vs calendar life.

Every once in a while running it down to flat or nearly so then charging 
again isn't a bad thing, it'll slightly increase the capacity (this is a 
real effect, we see it on unpackaged lipoly cells we use in robots, its 
not the memory effect, its something else, but a cell thats been sitting 
for a while or only lightly used will gain ~30% capacity with some 
"exercise") and more importantly let the fancy chips in the battery 
re-calibrate their calculation of the capacity of the battery.

generally discharging or charging cause damage, but the damage gets 
worse the further from the middle you go, when they want a really long 
life from cells, they run them just around the middle range, like from 
40% charge to 80% charge, with consumer lithium cells you will generally 
hit calendar life issues before cycle life if you don't go nuts.


btw the memory effect is a specific thing for nicad cells that was 
discovered when the batteries were discharged to *exactly* the same 
point over and over again (say 20% state of charge), then when expected 
to discharge past that point they had practically no remaining capacity.
http://en.wikipedia.org/wiki/Memory_effect#True_memory_effect

On 23/01/15 18:15, William Bennett wrote:
> Menno,
>
> Thanks for the information.
>
> I will add this: you'd be surprised how many computer experts,
> professionals included,
>
> labouring under this misapprehension.
>
> I asked around because I had been told of the existence of “memory”, but
> felt that the
>
> manufacturers should know what they were talking about.
>
>
> William.
>
> On Fri, Jan 23, 2015 at 4:42 PM, William Bennett <[email protected]>
> wrote:
>
>> So, having absorbed, from my friends,  the dangers of partially
>> recharging a  lithium-ion battery due to “memory”, I read the insert that
>> came with the new laptop battery:  –
>>
>> “Recharging a partially charged lithium-ion does not cause harm because
>> there is no memory. Short battery life is mainly caused by heat rather than
>> charge/discharge patterns.”
>>
>> Um, who's right?
>>
>> William Bennett,
>> Armidale.
>>

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