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”.