What's the deal with lithium ion batteries??

[prismejon]

Regarding almost all my earlier gadgets (cell phones etc.) I've been told that the batteries should be empty before charging, and when charging it's necessary to fully charge the battery - or else the performance of the battery would get dramatically worse.

Now I've heard the opposite about the lithium ion battery in my PPC: that it actually is better for the battery to be charged often and before it's getting empty.

Does anyone know what's correct? And maybe why the lithium ion batteries can support this?

[Duncan]

Ni-MH and NiCAD batteries (such as you are used to) have a 'memory effect' - i.e. if they are not mostyly drained then they 'forget' their full capacity and will not fully recharge.

LiION batteries have no memory effect (well, actually they do have a negligible one - but hardly noticeable). The reason why allowing them to fully drain is not a good idea? - when you do so the battery can need 're-condtioning' (two or three charges and discharges) to charge fully again - however, this is only an issue if you allow the battery to discharge and then leave it for a while (days) before the next charge. This 'psuedo' memory effect is not permanent - unlike with Ni-MH and NiCAD batteries.

This caution against allowing a full drain has became twisted into the myth that you need to charge often and before the battery has gone down very far (some even insist on charging at the 40% mark). This is unnecessary.

[msdawe]

My experience is that lithium ion and polymer batteries have a limited number of discharges as opposed to a "memory" like other rechargable battery technologies.

I purchased an iPaq 3650 in August or September of 2000 and a PCMCIA sleeve in December of 2000. I did much testing of the battery on the iPaq with discharges and such at one point trying to write a battery discharge timer. I discharged the battery in my iPaq many times but rarely did I discharge the battery in the PCMCIA sleeve. When I sold that package last week the iPaq battery needed to be replaced. After a day of sitting off charge with no draw (suspended, only memory drawing power) it woudl be at <60%. The PCMCIA sleeve on the other hand would be fine.

Basically, the PCMCIA sleeve which rarely got discharged still had a good battery after 2.5 years. The iPaq which was discharged many times because of my testing needed to have the battery replaced.

That goes along with what I was told about Lithium Ion and Polymer batteries.

Take it for what it's worth.

[Pony99CA]

LiION batteries have no memory effect (well, actually they do have a negligible one - but hardly noticeable). The reason why allowing them to fully drain is not a good idea? - when you do so the battery can need 're-condtioning' (two or three charges and discharges) to charge fully again - however, this is only an issue if you allow the battery to discharge and then leave it for a while (days) before the next charge. This 'psuedo' memory effect is not permanent - unlike with Ni-MH and NiCAD batteries.

This caution against allowing a full drain has became twisted into the myth that you need to charge often and before the battery has gone down very far (some even insist on charging at the 40% mark). This is unnecessary.
I read an article once that said that "deeply" discharging Lithium Ion batteries could cause crystallization which damaged the batteries (assuming I remember correctly :-)).

A :google: search didn't find the article, but did find an interesting discussion (http://www.allelectronics.com/cgi-bin/category.cgi?item=BTE-45) about this and related issues. A search here turned up Janak's Ultimate Battery Guide (http://www.pocketpcthoughts.com/forums/viewtopic.php?t=9063), which led to this page (http://www.technick.net/public/code/index.php?load_page=http%3A//www.technick.net/public/code/cp_dpage.php%3Faiocp_dp%3Dguide_bpw2_c10_06%26PHPSESSID%3Dfac48f3dfdc886a32f697732a65f0525) about prolonging battery life.

Steve

[Duncan]

The thing is - there are several conflicting accounts re. charging and discharging LiION batteries - I'm going on an account I read late last year which basically said the worries over deep discharging a LiION battery were greatly exaggerated and that the 40% requirement (as recommended by the link you give) is based on an out of date understanding.

Certainly deep discharging is a bad idea with LiION batteries - but then it is also hard to discharge a LiION battery to that extent (except by leaving a PPC to drain over a long period).

[Pony99CA]

The thing is - there are several conflicting accounts re. charging and discharging LiION batteries - I'm going on an account I read late last year which basically said the worries over deep discharging a LiION battery were greatly exaggerated and that the 40% requirement (as recommended by the link you give) is based on an out of date understanding.
If you're referring to the third link I posted (hard to know as you didn't quote my post or specifically state which one you meant ;-)), the only reference to 40% was for storing batteries, not discharging them.

In addition to cycling, the battery ages even if not used. The amount of permanent capacity loss the battery suffers during storage is governed by the SoC and temperature. For best results, keep the battery cool. In addition, store the battery at a 40 percent charge level. Never fully charge or discharge the battery before storage. The 40 percent charge assures a stable condition even if self-discharge robs some of the battery’s energy. Most battery manufacturers store Li-ion batteries at 15°C (59°F) and at 40 percent charge.
Steve

[Jerry Raia]

Glad we go that all cleared up. :mrgreen:

[Duncan]

If you're referring to the third link I posted (hard to know as you didn't quote my post or specifically state which one you meant ), the only reference to 40% was for storing batteries, not discharging them.

See - I quoted this time! :wink:

The reason for storage at 40% is because of the supposed inadvisabilty of discharging too far below 40%. Same reaoning in the end!

Frankly it would nice if I could recall the link I found pre-Christmas (which had the advantage of having come from one of the major battery manufacturers) but I don't have the link stored, Google won't show it too me and I can't even remember which manufacturer (memory like one of those things with holes in...). I did my original search precisely because I wanted a definitive answer as to how to treat my PPC batteries...

[prismejon]

Thanks for all the answers! :D