battery discharge

I have a compaq presario notebook with windows 98 2nd edition. when I unplug my computer to completely drain my battery, which is supposed to extend my battery life, the battery icon on the taskbar always indicates 100%, even after 4 hours. is that okay? I am concerned it might affect the shutdown process when the battery runs out. if it's just stuck how can I fix it to indicate accurately? thanks for anybody's help. Lgazele

 

Go to the Compaq website and search for software for your computer. They have a battery calibration program for your model.

Nickel-Cadmium batteries are very particular and exhibit a "memory" effect. If you discharge them only half-way and then fully charge them, they "remember" the half-way point as being the minimum and you have lost half your battery capacity.

These calibration programs not only reset the meter, but insure that the battery is discharged to its true minimum.

If you have a Nickel-Metal-Hydride batery, the memory effect is almost non-existent, but the meter still needs to be calibrated.

 

This is an interesting question. Computer columnist Bill Husted says he checked with some experts who say they do not see the memory effect in their laboratory tests. They see batteries worn out prematurely by excessive charging. So Husted does not recommend the periodic full discharge. He just says do not keep your batteries on the charger any more than necessary. His columns can be read in the Atlanta Constitution: www.accessatlanta.com/ajc Under print edition, click 7-day index. On the index page, his columns are found by clicking the business section of the Sunday edition. He sounds like he knows whereof he speaks. If anyone has more authoritative information, he and I would like to hear it.

 

Being a person who lives in a place with unreliable electric power, I have probably as many as 50 devices in my home, from the burglar alarm to smoke detectors, that run primarily on NiCad's.

Not all problems with these batteries can be ascribed to "memory ", to be sure. But I certainly believe strongly that the phenomenon exists. Maintaining these batteries becomes something of a religious ritual. I have some cordless phones that are over 8 years old that still hold a full charge for 3-4 days, depending how often they ring, and have never had their cells replaced. They are used to complete discharge between charges. People I know who keep their phones in the cradle are constantly replacing the batteries.

Overcharging is the biggest enemy of the NiCad. It eventually results in a rapid under-voltage that some equipment senses as battery failure, causing it to shut down when the actual battery capacity is still high. This appears to be a memory effect but isn't.

And too frequent complete discharges is also harmful. These are usually rated for charge/discharge cycles in the thousands, and each cycle shortens their lives.

And the worst thing of all for these batteries is series connections. When one cell in a series becomes discharged and the rest aren't, the dead cell can actually become reverse-polarized and is pretty much dead after that. So avoiding putting these things in a line greatly increases their useful life-span (when possible).

The care and feeding of these things is a nightmare. But since most devices require the voltages supplied by these batteries and Lithium ion batteries cannot supply these voltages, the consumer is pretty much stuck. Some Lithium cells are sold with a "dummy" so that they can be used in 3-volt devices in the place of 2 regular batteries. But before very long someone uses 2 of them and blows out the device in question. That is probably why most manufacturer's won't accept the liability.

Some of the newer organic polymer batteries, besides being easier to lift than the good, old, reliable lead-acids, can be taylored to wider voltage ranges. Hopefully, all our lives will be simplified in the near future by light, flexible batteries based on less wet chemistry and more of the physics of the solid state. Our laptop cases may actually be the battery.

 

You obviously have a lot of experience with these. You might be right. Husted always gets a lot of spirited discussion about those particular columns. The performance of your cordless phones is very interesting. But I never got that kind of performance when I was giving my batteries a full discharge on a regular schedule; and now that I have stopped doing that, I have not really noticed any difference. I just purchased a rechargeable maglite flashlight which said that the batteries should be fully discharged periodically, but said nothing about leaving them on the charger all the time being a bad habit. I think they got the priorities backwards. I am going to give this thing a full charge one day a week, so that it is always ready, and leave it off the charger the rest of the week, but not worry about the full discharge. It will be interesting to see what kind of performance I get.

 

Sorry to hyjack this thread fellas but this is an interesting topic which is never clearly addressed by the manufacturers .
I have been given a laptop which previously had a working battery that held a charge.
Although the battery was lefton charge 12 hours it is not holding sufficient charge to start up. On switch on it starts to boot and then beeps and switches off.
I have never used a laptop before. How long should you charge the battery for ? How can I test the battery to see if it is US

 

12 hours should certainly be enough. And those sealed units can be ruined by a single bad cell. I have opened them before and used a voltmeter to identify the bad cell. But replacing one is usually a short-term solution since another goes soon after. And the results aren't pretty.

The trouble with some of these packs is that they also are center-tapped somewhere, providing 2 different voltages to the laptop, but essentially providing a double-whammy regarding the series connections I mentioned above. Their lifetimes are shortened considerably by this ingenious machination.

A procedure which I saw recommended, but don't recommend myself since it has failed 9 out of 10 times, is to locate the offending cell and apply a relatively high voltage to it for a short time. Some of these devices on the market have used capacitors to give the offending cell a sudden jolt. Others have used a straight 12 volts.

The theory was that tiny metallic bridges formed in the battery and shorted the anode to the cathode. This temporary jolt was supposed to burn out these shorts. It has worked for me only a couple times, but I still try it before forking over $50 or so for a new pack.

I was fortunate to have received a gift from someone who did not know what the device was---a portable, sealed lead-acid power supply that gave voltages from 3-12. It is about half the size of a lunchbox and has multiple connectors. I use it for radios, laptops, lanterns, and most anything else for which it isn't too inconvenient. It outlasts my laptop battery by 4-5 times. If you see one of these things, grab it. It's a little something extra to carry around, but a very nice reliable source of portable power.

They pretty much have us caught between expensive packs that function poorly, cost a lot, and last a short time, and carrying an external supply.

Duke --as time has gone on, the chargers that are supplied by manufacturers, particularly those for phones, have become better at sensing a full charge and not continually supplying the over-voltage necessary for charging. These chargers shut down when the battery is charged and cause far less harm than the older ones. They cost more, of course, but if you have that type of gradient charger, leaving the device on the charger does little harm. That may be why it is not mentioned with your phone. I'm sure the feedback they got from people who were constantly replacing the batteries (since many people store the phone in the charging cradle) led to improvements.

 

Wow thanks abraxas - now that's what I call a rely!...

I hadn't thought of opening the battery so I'll try that next.
he says realising that he's left his trusty multimeter in a friends house miles away,
This is a huge great 12v 4mah beast and is the very last battery on the list and the most expensive. £80.00 Just my luck!

I had thought of getting a smaller laptop or general rechargable battery pack that fits in the space and hardwiring it, say a remote control car type or even soldering together some rechargable bateries! I guess it should work but won't have anything like the endurance.
I'll try your suggestion thanks
Nick

 

Places like Radio Shack sell the replacement cells with solder tabs on them. If you get the thing open without decimating it, you may get away with replacing 1 or 2 cells.

 

The "memory" on batteries has been over-rated and repeated incorrectly. Even the old ones that do have a "memory" it's not every time. If you run down the battery say, half way, then recharge. That doesn't set the memory. If the battery is continually drawn down half way, after a while it may effect the battery. Run the battery down half way a few times, then every once in a while run it down completely (if your worried about it).
So even if you do have some old batteries that have a "memory effect" that still doesn't mean that you have to run them all the way down EVERY TIME.
Unless the test or experiment is controlled, you can't draw a correct conclusion on a battery. I have done controlled tests on rechargeable batteries and have found that it is true that overcharging is the most problem, and the "memory effect" on older, first generation re-chargeable batteries is over-rated and misunderstood (it's not every time. In fact, if you read some manuals CLOSELY, it will even say "don't REPEATEDLY subject the batteries to partial charges).