The really dumb thing is that, as far as I can tell, a battery's controller generally counts a "cycle" as "started discharging, started charging", regardless of time in between. At least, that's how it was with my MacBook a few years ago. Unplug, plug in, cycle count increases.

The crappy thing about that is warranties. Apple, for example (at least last I checked; I don't use a Mac anymore) , would replace a battery if it had under some number of charge cycles (and presumably was less than a year old), but not if it had more than that number.

That means that if you treat your battery really nicely by always keeping its charge between 40% and 60%, and it turns out to be defective, they probably won't replace it because of how many "cycles" it has gone through.

Of course, those kinds of cycles have very little to do with the longevity of a Li+ or LiPo battery anyway. A better metric would be total energy output over time, which would be far simpler to calculate anyway.

I don't believe that description of cycle count has ever been accurate for Apple hardware and certainly isn't for recent MacBook Airs:

http://support.apple.com/kb/HT1519

Yeah it definitely doesnt, I have had and used dozens of macbooks and you cant ever plug in and out and see your charge cycle increase each time. I usually have my laptops 1-2 years and they rarely go above 300 charge cycles per year, and I usually dc my laptop 5-10 times a day.

If you read the documentation a cycle is considered a full charge and discharge of the battery. It doesn't have to be discharged or charged fully, but when you've charged the full capacity of the battery and discharged that same amount, that's a cycle.

Sure, but that was not reflected in System Profiler when I actually tested it. Unfortunately I can't test it again now, as my old MacBook's battery will hold up for approximately 14ms before the computer shuts off.

A battery engineer would view that as a cycle, but Apple does not.

Funny thing is, I don't imagine any li-on battery lasting 1000 cycles after full discharges! Good warranty or what!?

As they say in the renewable energy field: the majority of batteries do not die peacefully, they are murdered.

As a bit of a re-assurance, the typical laptop power circuit in a laptop using lipo is aware of this and will simply refuse to drop the battery below a certain level so likely the damage is somewhat limited. Still, if you don't need to discharge a battery all the way as far as the circuitry will let you with lipo's you'd better not.

> opposite of Nickel Metal Hydride

Fully discharging any battery isn't good for it. NiCd had the particular problem of "memory" developing though, so going through a full discharge cycle was necessary to prevent the memory forming. It wasn't good for the battery, but it was better than letting the memory develop.

I'm not aware of NiMH developing a memory, so that wouldn't be a good thing to do with NiMH either. I always tried to avoid full discharge of my NiMH batteries and always got a pretty long life out of them.

Really the full discharge cycle is an artifact of the needs of one particular chemistry (NiCd) that became something that "everybody knows" you should do long after it became counterproductive.

There are two types of discharge states - typically "fully discharge" implies within the application the battery was designed, not completely dead. For example, a car battery is fully charged at 12.6v, but discharged at 11.2 (or somewhere around there). There is still lots of capacity left, but dead for the use of cranking over an engine. NiMH typically has a very fast self discharge rate - letting these dip well below the operational capacity level will be much more detrimental than just letting your drill die after prolonged use.

NiMH has memory too, but not as bad as NiCd. We always suggested allowing NiMH to fully discharge time to time, but we never suggested keeping a phone on its base constantly.

Both these types of batteries need to be primed properly - full discharge/recharge the first few cycles. (Not sure about the new pre-charged NiMH, like Eneloop)

Memory builds faster when left in a discharged state.

Cadex machines can be used to reverse memory, to an extent.

I'm speaking from memory from 6 years ago. Hopefully I didn't mess up too much =P

There is occasionally a need to do a full or nearly full discharge on Li-Ion batteries in order to recalibrate the state-of-charge indicator if the embedded controller gets confused, or if the battery is nearing the end of its usable life and has significantly diminished capacity.

But in general, deep discharges are bad for any electrochemical cell, and should only be done to prevent or forestall something worse.

NiMH cells shouldn't be "topped off" when they're nearly full, but that doesn't mean they should be fully drained before charging.

I believe you are correct on the "cycling the battery", which I believe you want to avoid, so that you battery will be able to charge fully for longer.

"A charge cycle means using all of the battery’s power, but that doesn’t necessarily mean a single charge. For instance, you could listen to your iPod for a few hours one day, using half its power, and then recharge it fully. If you did the same thing the next day, it would count as one charge cycle, not two, so you may take several days to complete a cycle. Each time you complete a charge cycle, it diminishes battery capacity slightly, but you can put notebook, iPod, and iPhone batteries through many charge cycles before they will only hold 80% of original battery capacity." - http://www.apple.com/batteries/

http://support.apple.com/kb/HT1519

There are mixed meanings in the definition of "cycle", but both make sense, just depends on the context. Thanks for the blurb!

He does state "letting the battery" cycle, so I'm assuming he is implying the battery is being allowed to be discharged near fully.

Interesting. Last I looked, the supposed optimal way to prolong a Li-Ion battery was to not let it get below 50% (ie, plug it in to charge when it gets to 50%). I think it was from a link off of Lifehacker a while back. Storing at 40-60% was recommended as well.

I do typically use a smart charger on my NiMHs, and make sure to "break-in" (full discharge -> trickle charge to full -> full discharge -> trickle charge to full) every three months (12 for the new LSDs); I've managed to keep some AAs for well over a decade doing that, albeit I have plenty of spares, so I cycle through them and most are kept at room temperature storage. I used to freeze, but read that that might not be good for them long term (not to mention you have to wait for them to warm up before you can swap, defeating the purpose of spares; also, there's the possibility of thermal shock if you don't warm them up slowly/gently in the fridge).

I too read the 50% capacity rule, but I read it in a very professional battery book, but I remember the gains were very minimal. Something like 10-15% increase in lifespan. When a battery is only lasting 2-3 years as it is, that is less than half of a year.

Going back to my link, it looks like 50% is the sweet spot in the DoD chart; multiplying the number of discharges by the DoD results in 50% DoD being the highest return on capacity.

But...also remember in an application where you can use the device while its charging changes the concept of maximizing life span. I don't believe the act of discharging will avoid shortened lifespan, but rather it avoids degradation on the battery CAUSED by discharging itself.

Batteries hurt my brain...

Wouldn't all modern power management ICs operate the laptop directly from the power supply while float-charging the battery resulting in negligent amounts of heat?

Yes to the former, but (hopefully a real battery expert can chime in here) my understanding is that lithium-ion batteries cannot be float/trickle charged safely. Their internal resistance is too non-linear and it's too easy even with a "full" battery to provide a voltage that will sink dangerous amounts of current and overheat.

All lithium ion technologies I'm aware of require active current and temperature monitoring.

Probably 90% of the time I'm using my laptops is when I'm actually sitting at my desk and they are always plugged in at that time. I recently read where someone else had stated that it was good to remove the battery (if you can) if using the laptop with external power.

Any idea if this this accurate or will prolong battery life? I've got an (almost) brand new Thinkpad with a large, expensive battery that I'd like to preserve as much as possible (like anyone else).

I don’t know if this applies to other notebooks but at least Apple used to recommend that you do not remove the battery [0]. There’s a little more discussion on Super User [1] but there seems to be no definite answer.

[0]: http://web.archive.org/web/20130615084258/http://support.app... [1]: http://superuser.com/a/12842

At least some Thinkpads used to let you limit the charge on the battery.

Capping the charge at something like 60% is a great way to preserve the battery if you're not going to need all that battery life.

Storing at 40%-60% elongates the life compared to 100% or 0%.

All of this is 2nd hand, and I have no particular expertise to validate this comment.

I don't understand. So with this setting people are artificially limiting their battery capacity to 40%, in order to preserve capacity they're not going to use? Meanwhile you'd have to ride a battery pretty hard to grind it down to 40% health, it'd take many years probably.

I'm not sure what the average lifetime of a laptop is, but I'd be surprised if it's more than 8 years. What's the upside if the battery is well preserved at the time when the device is being replaced? Let's say with normal usage the battery will perform at an average of 80% over its lifetime, that's still better than 40% - for the same money.