Lithium-Ion battery care
February 5, 2011 3:59 PM   Subscribe

Talk to me about Lithium-ion batterys on my iPhone and iPad. Seems to be many vague opinions on care and maintenence, 'discharge fully once a month, but charge frequently', etc. I currently aim for charging when it hits near 40-50% if I'm near a outlet. What's your take on how to best make these batterys live longest?
posted by BVB to Technology (19 answers total) 8 users marked this as a favorite
 
Farhad Manjoo did an interesting piece in Slate on this about a year ago.
posted by argonauta at 4:03 PM on February 5, 2011


I'd go with Apple here

Use iPhone Regularly
For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Be sure to go through at least one charge cycle per month (charging the battery to 100% and then completely running it down).

posted by jourman2 at 4:08 PM on February 5, 2011


Yeah, those pesky electrons getting lazy...

I don't see where completely running a battery down can be a good thing that you should do on purpose. It is like saying "completely remove and refill all the air from your tires once a year". Batteries are chemical devices- every time you use them, you wear them out. Not nearly so much with Li-Ion batteries, apparently, but it still happens.

But the truth is, as far as I can tell from reading things from people who know these things, is that Li-Ion batteries have a set lifespan of so many years from the time of manufacture. As soon as they are put together, a chemical reaction clock starts, and they are going to drop dead 5-ish years later. (Or thereabouts. The cells are likely a lot older than the thing they are in.)

If you are lucky- because since most "batteries" are made up of multiple cells, if any one of them dies an early death, the whole battery pack is toast. That's what ends up killing most batteries, in my experience.

Speaking of my experience, my rule is "if I use it every day, I charge it every night". And "never leave it sitting on a charger once it is charged (or unplug it the next morning)". And "never run them flat". My batteries last a pretty long time. Could be coincidence, but probably not.
posted by gjc at 4:27 PM on February 5, 2011




Some kinds of rechargeable batteries, most notably NiMH and NiCad, are subject to "memory effect". What that means is that if for a while you only use a certain part of the chargeable range, eventually that's the only part that works. So for those technologies it really is important to fully discharge the battery (which isn't really fully discharged, but that's for another day) every once in a while, so that the whole usable range continues to be usable.

LiIon batteries are only weakly susceptible to the memory effect. When you first get a device with such a battery, it's worthwhile to fully charge it and then let it fully discharge, but after that you pretty much don't have to worry about it.
posted by Chocolate Pickle at 4:40 PM on February 5, 2011


I don't know precisely what kind of lithium battery is in the iDevices. But, lithium polymer batteries must absolutely not be deep-discharged. In general, in smart electronics, the power management is good enough to prevent you from really discharging them to dangerous levels. But, completely discharging a lithium polymer battery will completely kill it. Like, forever.

(They're used widely in RC vehicles. And nothing kills a $300 battery quicker than running it down to 0% charge.)
posted by Netzapper at 5:03 PM on February 5, 2011


But, lithium polymer batteries must absolutely not be deep-discharged.

That's true for all lithium batteries. But usually there's circuitry built into the battery itself which prevents that.
posted by Chocolate Pickle at 5:05 PM on February 5, 2011


I tend to remember to let the battery on my iPhone die about once a month. I tend to sync my phone every night so it will have a fresh charge in the morning and be all synced up. I have no idea what the battery percentage is when I plug it in at night unless I've been using it a lot and got a low battery warning. Every once in a while I'll forget and the phone won't get recharged overnight and I'll have to charge it the next day.

When I was working where I was using the phone a lot (streaming Pandora, playing music in the iPod app, browsing the web) I'd keep the iPhone plugged in at my desk all day so taht I could listen to the music and still have a full charge for the bus ride home. In that time, I didn't notice any ill effects.

LiIon batteries have a limited lifetime and I'm usually onto the next phone by the time I've had to worry about the battery needing replaced. EXCEPT! Heat will take the cycles off the life of the battery way faster than charging/discharging habits. Avoid leaving the phone/computer/etc in a hot car.
posted by birdherder at 5:28 PM on February 5, 2011


The battery for my 12" Powerbook is over 5 years old and still holds a charge, but I woudn't want to rely on it...

The charging and emptying is for calibration - it doesn't extend the life of the battery, it allows the device to gauge battery life more accurately to tell you how much time you have left. Battery life is limited by the capacity of the cells and oxidation, which limits the ability to deliver charge, although with relatively low-power devices that's not such a huge issue.

For the small batteries in mobile devices, I wouldn't worry too much about it, to be honest. There's every chance it will keep most of its capacity up until a new iPhone or iPad comes out and you replace it. If not, I'd just use it until the battery gets flaky then have it replaced in an Apple store.
posted by DNye at 5:42 PM on February 5, 2011


DNye: The charging and emptying is for calibration - it doesn't extend the life of the battery, it allows the device to gauge battery life more accurately to tell you how much time you have left.

There's your answer. The battery gas gauge tries to estimate the amount of remaining energy by measuring the current going out of the battery when you operate the device and the current going into the battery when you charge the device. It's like trying to estimate how full your gas tank is in an old Volkswagen with a busted gas gauge by how far you drive and how much gas you pump at the station over a period of months. It is reasonably accurate but once in a while you have to fill it up and drain it to the minimum to re-calibrate available driving distance.
posted by JackFlash at 6:45 PM on February 5, 2011


+1 for the Battery University link above- note this paragraph:
Although lithium-ion is memory-free in terms of performance deterioration, batteries with fuel gauges exhibit what engineers refer to as "digital memory". Here is the reason: Short discharges with subsequent recharges do not provide the periodic calibration needed to synchronize the fuel gauge with the battery's state-of-charge. A deliberate full discharge and recharge every 30 charges corrects this problem. Letting the battery run down to the cut-off point in the equipment will do this. If ignored, the fuel gauge will become increasingly less accurate.

When they say "full discharge," that does NOT mean running the Li battery down to close to zero volts- the "cut-off point" is typically around 2.7 volts for a single-cell lithium, and the protection circuit either in the equipment or in the battery itself will stop current flow at that point. Charging circuits for lithium batteries are pretty complex and, um, "intelligent."
posted by drhydro at 7:24 PM on February 5, 2011


The battery gas gauge tries to estimate the amount of remaining energy by measuring the current going out of the battery when you operate the device and the current going into the battery when you charge the device.

No, what it measures is the voltage. They maintain a curve in memory of what voltage represents what percentage discharge.
posted by Chocolate Pickle at 7:27 PM on February 5, 2011


what it measures is the voltage. They maintain a curve in memory of what voltage represents what percentage discharge.

No, this isn't the way it works. The voltage-capacity curve is almost flat between 10% and 90% full and gives you no reliable information on the state of charge.

Battery gas gauges actually integrate the voltage produced by the current through a sense resistor, what is called a coulomb counter. This is a measure of the current into and out of the battery. This voltage is produced by the current through the sense resistor which changes second by second, not the voltage across the battery terminals which is almost unchanged for hours between 10% and 90% of battery charge.

The terminal voltage curve, which gets steep both near full battery and low battery helps to determine full and empty, but they use the coulomb counter to determine intermediate values of charge. This is why you need to periodically recalibrate the coulomb counter. Integration of small current changes, plus and minus, over many small cycles leads to errors, the same as integration by inertial navigation devices need to be re-calibrated periodically. Meanwhile, the terminal voltage is almost unchanged over this intermediate battery charge range.

Notice that right after you turn on your laptop and fire up a couple of applications, that the battery gauge will indicate maybe only a couple of hours of battery time left. This is because the boot-up process uses a lot of current and the coulomb counter integrates that to indicate a rapid rate of discharge. After a few minutes of slow browsing or idle, the battery gauge will indicate more hours of battery life because the coulomb counter detects a slower rate of discharge and projects a longer battery life. Between these two measurements, a few minutes apart, the voltage of the battery terminals has not changed at all. What has changed is the current measurement by the coulomb counter.

The same sort of system works in your car if you have a computer gas gauge that indicate the number of miles left in the tank. If you drive stop and go for a while, the projected mileage goes down, but if you drive at a steady pace, the projected mileage goes up. The computer determines this by integrating the actual amount of fuel being injected into the cylinders (the equivalent of current above), not by measuring the level of the fuel in your tank (the equivalent of terminal voltage).
posted by JackFlash at 8:46 PM on February 5, 2011 [1 favorite]


Actually, cars use both the fuel level and average fuel economy to estimate the remaining miles - the fuel level to determine how many gallons of fuel there is, and the average fuel economy to convert those gallons to miles. The ECM does sum the fuel delivered per distance traveled to come up with fuel economy. Usually the average fuel economy used here is less filtered than the displayed average fuel economy.
posted by rfs at 9:25 PM on February 5, 2011


Li-Ion. Don't run them at full charge all the time. Something about the makeup says having them at 75% or something is healthier.

Discharge them fully (not fully as in nerd-attaching-resistor-to-terminals fully - but just run them right down) once a month or so - not a big deal.

Your worst enemy is heat - but if you can't do anything about it, dont' worry about it, and enjoy your device.

Chance are you will accidentally destroy it, get it stolen, or be ready for a new one before the battery life gets low enough for you to be really annoyed (and at that point, you can always fork out a bit fo ra new one)
posted by TravellingDen at 9:32 PM on February 5, 2011


Incidentally, its pedant's corner, but the batteries in your iPhone and iPad are Lithium-Ion Polymer (Li-Poly) rather than Lithium-Ion (Li-Ion). Traditional Li-Ion cells are made of rigid cylindrical cells - if you crack open an old laptop battery it will have things shaped like regular batteries inside it. Li-Poly cells are polymer pouches, so they can be a wide variety of shapes. It doesn't make a huge amount of difference in terms of charge, though, unless you're leaving a battery-powered device charged but unused for a long time and then coming back to it and wanting it to have kept its charge.
posted by DNye at 7:19 AM on February 6, 2011


It's pedant's corner, even. Secret of comedy.
posted by DNye at 8:17 AM on February 6, 2011


Thanks for all the great responses! I think I learned alot about batterys here! Bottom line, just use them! Run 'em only occasionally, and don't leave them to over charge....Thaks to all!

BVB
posted by BVB at 11:00 AM on March 10, 2011


oppps! "run them *down* only occasionally"....
posted by BVB at 11:01 AM on March 10, 2011


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