I recently bought a Pocket PC and it uses a 1440 mAh Lithium-Ion Removable, Rechargeable battery. I began recharging my pocket pc when the battery had about 60% of its power left because I wanted it to be full for the next day. Some people mentioned that they thought recharging a filled battery was very bad and you need to wait for it to be completely empty. I wasn’t sure if this was true because I didn’t see it in the owners manual and I figured maybe this Lithium-Ion battery didn’t operate like that? Any ideas what the truth is? Thanks.
Nickel Cadmium rechargeables are that way. They have what is called the “memory effect.” Partially discharging and then recharging them as a habit works them into a state where they act like they are empty when you’ve discharged them to the point where you would normally recharge them.
Other battery types don’t have this problem - they have their own.
Nickel-Metalhydride batteries have a limited life. About 500 charge/discharge cycles are all you can expect, and if you have to draw high current from them they won’t even make that.
Sealed Lead/Acid batteries have their own special problems. They are picky about charging rates and don’t like deep discharge. They also tend to die permanently if you leave them unused for too long.
Lithium based batteries have a limited life span. After about three years, a lithium base battery will have permanently lost about half of its capacity. When a three year old battery is fully charged, the device using it will only run about half as long as when used with a fully charged new battery. It does not matter if the battery is used during those three years. If you buy a new battery that has been sitting for one year, then it will only be two more years before it has lost half of its capacity. Lithium batteries are the pickiest of all when it comes to charging. The battery packs have their own built in processors to manage the cells - it is almost impossible to buy individual lithium cells, you have to buy a complete pack with a housing and the charging circuitry.
No battery is perfect.
Don’t worry about recharging your lithium battery before it is run flat.
its generally referred to as “battery memory” the battery manufacturers claim it doesn’t exist anymore, but I beg to differ.
Mort Furd’s post is a great one and i personally will hang on to it for reference. however, I will also continue to run my batteries down all the way before re-charging.
Never let any rechargable battery run “flat” or “empty”, i.e., to zero volts. Running them down to where the device will basically no longer work well is best. This is well above being completely discharged.
I have no experience with Lion batteries, but with NiMH batteries, they can be “overcharged”. I.e., you keep them in the charger even though they are fully charged. The battery then starts to lose power. So a “60% charged” may mean that it has 40% more charging to go, or that you have in fact overcharged it. The solution to overcharging is to run the batteries down, charge them just right, lather, rinse*, repeat, a few times. I brought a NiMH back from at most 10% charged to 96% this way. But cycling reduces lifespan so overcharging should be avoided.
Avoid trickle charging once it’s charged.
*I hope no one actually …
That’s not what Cecil says!
Now, who do you think I am going to believe?
Yeah, ftg. Never let a battery run down to zero volts. Sorry, I should be more precise. By “flat,” I meant “until the device shutdown and won’t run.” Most devices have some kind of system to detect this, and others just screw up so bad the user shuts it off in disgust.
The Metal-Hydride thing is something I’m especially proud of. My company did a lot of work to determine why batteries were failing prematurely - even though all the battery analyzers were giving the batteries a clean bill of health.
Our customer had a lot of two-way radios with metal-hydride batteries. After a few months, they started bringing in radios that would give a “low battery” alarm every time you transmitted. Our battery analyzers were reading full capacity on the batteries, but you couldn’t transmit with the radios.
It turns out that you can put a heavy load on a metal-hydride battery (5 watts of transmits power for this radio=2Amperes discharge current for the battery,) and it will cooperate - for a while. After a while, the internal resistance of the battery climbs to the point that it can’t deliver high currents anymore - and the radios complain.
We figured this out by making measurements of “bad” batteries and new batteries. To finally prove it to the radio manufacturer and the battery analyzer manufacturer, I tested a bunch of batteries to destruction. We ran a simulated use cycle on a group of batteries every day and night for a couple of months, and documented each discharge cycle to show discharge current, voltage, and internal resistance of the battery. I wrote the test software and did all the work.
The battery analyzer manufacturer made a software change and added an internal resistance test to quickly check metal-hydride batteries. The radio manufacturer never admitted to having a problem. They gave us a bunch of higher capacity (110% of the old ones) batteries to replace the “bad” ones - and the higher capacity batteries died even faster.
The thing is, the “bad” batteries weren’t really bad. They just refused to be operated outside of their ratings. The radio manufacturer was selling the radios by advertising them as the world’s smallest radio with 5 watts of transmit power - and the small size came in part from have a small (physically and electrically) battery. The standard battery (600mAh) was underrated for that power level, but the only way to get the touted small size was to use the standard (small) battery. They made 1500 and 1800 mAh batteries for that radio, but they were as large as the radio itself.
We finally told our customer to either use a lower transmit power or use the high capacity Ni-Cad battery for high power.
You should not discharge a metal-hydride battery at more than 20% of its rated capacity. If it is rated for 600mAh, then don’t discharge it at more than 120mA.
Two things:
- In general, the less “deep” you discharge your batteries, the longer they’ll last.
- The manufacturers are correct when they say the memory effect in NiCAD’s is (more-or-less) non-existent.
Mort Furd, I have some experience with batteries and I agree with you that many, if not most, gadgets (cameras, laptops, etc) have batteries which are just to darn small for the device. But manufacturers know what sells and things that are large because of bulky batteries do not sell.
I was recently discussing digital cameras and their batteries with a friend who is shopping for one and was explaining that the bigger the battery, the better. He asnwered that the object of the camera was not to be efficient but to please his wife so the cool factor came first and he bought one with undersized batteries. And this is a couple who complain their video camera has lousy batteries and is worthless. . . but it is cool because it is tiny.
I’m not talking about a battery being too small for a useful operating period. I’m talking about too small as in “capable of damaging the battery too small.”
A larger capacity battery used on the radios I mentioned above not only runs longer on a single charge, the life of the battery is longer because it isn’t being forced (as far) out of its capability. The customers who used the 1800mAh metal-hydride battery never had premature battery failures - and everyone who used the standard 600mAh battery had failures within 6 months.
As far as Cecil and Ni-Cads:
Phooey.
Blasphemy, I know. I also know how many batteries I’ve rejuvenated from the memory effect.
OK - how, EXACTLY does one rejuvenate a dead Ni-Cad?
I’ve got bunches of 'em - and these ARE batteries, NOT cells (camera motor drive packs, etc)
thanks!
very good info Mort Furd. In general NiCd or NiMh should be cycled to 100% depth of discharge (fully depleted) to avoid voltage depression (what is commonally called memory but isn’t technically true). With Nimh you have more cycles to play with before memory becomes an issue but it will.
Li batts are a little different, when manufactured the cell will start eating itself - there is no way to stop it short of storing it in liquid heliumn. What ever you do charge wise it will most likely die on a particular day 2-5 years from the manufacture date.
You mean fully discharging the battery first will prevent over-charging, right? But if you have a “smart” charger, it will stop charging when the battery is full so I don’t think it would make a difference. I’ve seen manuals that say you should use up the battery before recharging, but only on devices that come with “dumb” (timer operated) chargers.
I just did a google search. It seems half the sites recommend fully discharging NiCADs while the other half claim that fully discharging them is damaging.
What’s the truth? Wish there were some scientific articles on this subject.
I’m no battery expert, but it would seem to me that purposefully fully discharging a NiCAD is usually a bad idea. This site agrees. But may others don’t.
This is from a NiCAD FAQ:
and
But it also says
If we are to believe this FAQ is in any way authoritative, then I guess we should conclude that occasionally deep charging a NiCAD is O.K. (and may even be beneficial), but routinely deep charging them is a bad idea.
My understanding is that if you completely discharge a battery, it will cause damage. On some devices it’s easy to do accidentally - bicycle headlights, for example. But most electronic devices have a cutoff circuit that shuts off power before damage can occur, so on such devices it’s usually harmless to use the unit until it shuts down. And some devices come with “dumb” chargers that cannot properly deal with a partially used battery, so the manual tells you to use up the battery before charging.
For any cell in a battery, the manufacturer specifies a discharge limit. In normal operation, you should never go below that limit. If you do, you risk damaging the cells and you risk voiding any warranty you may have had on the battery.
Fully discharging (down to zero volts) any battery can damage it. Don’t do that. A Ni-Cad “likes” to be discharged to its lower limit - usually 1.2Volts. A lithium battery can’t be discharged past its lower limit - the built in charging circuitry guards against that. Metal-hydride batteries don’t mind if you don’t discharge them to the lower limit before you recharge them.
Extraneous:
The right way to do the job is with a battery analyzer. These are microprocessor controlled devices that slowly discharge the Ni-Cad battery to 1.0Volts per cell. The processor constantly monitors the current and voltage to watch for problems and abort the process if something goes off track.
It is possible to do it manually, but there is a chance you’ll permanently damage an otherwise salvagable battery.
There are inexpensive analyzers available, but be careful in what you buy. A real cheapy will just discharge the battery to 1.0V without any further monitoring. These run the same chance of damaging the battery as doing it manually.
Also, a lot depends on what the problem is as to whether or not you can rejuvenate a Ni-Cad.
If it has simply reached the end of its life cycle then there’s nothing to be done with it.
If it has the memory problem, then running it through an analyzer will get it back to very near its original capacity.
If it has been improperly stored, a crystal might have grown and punctured the insulating layer in the cell causing a short circuit. The analyzer will tell you that this has happened, but not what to do. I’ll not tell you either, because it is dangerous and because you will have to know and remember how to deal with that battery for as long as you own it.
Here’s a previous discussion we had on this subject:
http://boards.straightdope.com/sdmb/showthread.php?threadid=153903
There is some info on extreme rejuvenation tricks on NiCads at the Repair FAQ web site. I have tried a couple of them with at best partial success. Note that the page basically doesn’t say much about NiMHs, let alone LIons.
(I just realized today that I was calling Sam Goldwasser “Sam W.” instead of “Sam G.” in recent posts. Mea culpa.)