Care and feeding for your laptop battery

A Friend and I were discussing laptops, in particular Apple Powerbooks. He recently acquired a Powerbook from his work, plus he has an old G4 under his desk, used as a server. He usually has insightful comments, so we often have conversations about this and that new geek gadget. During the discussion we started talking about battery life and the best way to charge. I purchased a R30 for my brother two years ago with an additional Ultrabay battery. It still often gets 8+ hours of hard office-type use running WinXP. Every comment I’ve read and my experience has show that IBM hardware kit just works. This should be the inspiring goal for any laptop battery system. Although following the “Conservation of Greatness” rule, I’ve been told the IBM’s service often sucks. Luckily I’ve never had to deal with them.

Anyway we started discussing batteries, and how to best care for your battery. Based on a page I’d read several years ago I’d always been of the opinion with Lithium Ion batteries, that constant charging is a good thing to do. This page had stated that Li-Ion batteries have a finite number of ‘deep’ discharge cycles. Thus it was better to keep the battery charge to preventing the ‘deep’ discharge cycles occurring.

Richard’s opinion was the opposite of this:

“Nah I got into talking with a laptop guy on this one, and it’s the continuous connected to the mains stuff that destroys them. Doesn’t matter the battery type, if it’s continuously trickle charged it will die.”

I figured it was time to do some goggling.

First search result was a page on Rechargeable Notebook Batteries – Shelf Life and Notebook Battery Maintenance Tips. It gave the following guidelines:

The most important thing to understand about laptop batteries is that they are always losing a small bit of their charge. (…) The second most important thing to understand about notebook batteries is that their capacity decreases with each cycle of charging and discharging (or usage). By itself, this is not surprising – but when combined with the previous point, it leads to a surprising conclusion. When laptop users leave their laptop battery inside the machine but leave the computer plugged into the wall, the laptop battery is going through a constant charge-discharge cycle.

A later site, provided further insight. It reiterative the above, also covering an improved version clearing my earlier misunderstanding:

Charge often. Don’t try to fully discharge the battery packs frequently. This only adds strain. Several partial discharges (regular use) with frequent recharges are better for lithium-ion than one total discharge. Recharging a partially charged lithium-ion battery pack does not cause any harm because it has no “memory”.

So in contra to my previously held brief, it is best “not to leave your laptop with its battery constantly charging” plugged to the mains. Li-Ion do have a finite charge cycle amount, but it is for any charge, not just deep cycle charges. Plus the constant heat generated during charge causes damage to the batteries.

Li-Ions have no memory, so its either better to not to leave your laptop plugged into the mains, and let the battery discharge until it gets to 50% before charging against. Or if you want to use it constant from one location remove the battery and leave the laptop on mains. In fact the latter option, also helps the battery further by preventing by reducing heat-wear.

I wonder why no vendors has thought to added the following profile battery options to power management: “Constant Mains”, only charge battery if below 30%; “Getting Ready to Leave”, only charge battery if below 95%; and “Keep Over X% charged”.


  1. Richard Parry Said,

    January 29, 2005 @ 6:17 am

    I wonder why no vendors has thought to added the following profile battery options to power management: “Constant Mains”, only charge battery if below 30%; “Getting Ready to Leave”, only charge battery if below 95%; and “Keep Over X% charged”.

    I suspect it’s because vendors, at the end of the day, get to make serious cash selling you a second, third, or fourth battery. Whilst this sort of functionality would be great from a usability point of view, it might also end up lengthening the life of the battery.

    Also, vendors would like to sell you a second battery for constant use anyway – so that you always have a fresh spare fully charged.

  2. Nicholas Lee Said,

    February 9, 2005 @ 7:55 pm

    An additional page with some very good information on battery care.

  3. BigZaphod Said,

    February 10, 2005 @ 1:48 pm

    I don’t quite know about this. I had a G4 1Ghz PowerBook for 2 years. I almost always used it with the power plugged in (while sitting on the couch, at work, etc). After 2 years my battery was still holding about 2 hours of charge. (I just sold it today, actually, as I now have a new 1.67Ghz PowerBook :-)) A friend of mine who got his PowerBook at the exact same time as me (we ordered on the same day) has just replaced his battery as it was unable to hold a charge for much more than 20 minutes. His usage pattern was usually on battery power and only charged when it was getting low. Based on my experience, it seems it is far better to keep it plugged in than not. Admittedly, this is a small sample. 🙂

  4. Nicholas Lee Said,

    February 10, 2005 @ 2:12 pm

    Apple themselves state “Apple does not recommend leaving your portable plugged in all the time.” So you must have got lucky. 8) Of course if its frequently deep cycle discharged I think that a battery can decay faster. I’d be interested in what the calibrated battery life on your new Powerbook is when its used for normal activity. Say browsing on the internet over wireless.

    One of things I think is a shame, is that Apple do not offer a high capacity battery. IBM have a 6-cell and a 9-cell battery with the later giving at least an extra of battery time.

  5. Suhy Said,

    May 12, 2006 @ 1:17 am

    I was researching thil also….
    i got information that:
    Li-Ion do have a finite charge cycle amount, BUT, charge cycle is not the same as it is at ni-cd ni-mh batteries.
    At ni-cd charge cycle is : plug battery to charger, unplug the charger when is full – that means, that when you charge battery, there goes 1 cycle
    At Li-ion charge cycle is : plug battery to charger at 75%, unplug the charger when is full. That is not a cycle. That is 1/4 of cycle.
    -that means that 1 cycle is when battery is charged 100%(it doesn’t matter if it does this in time of charging from 0 to 100% or during 5 charges from 80-100%)

    that is what i heard..
    if this is true, than it is best to have battery always on charge if possible

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