# Charging laptop batteries



## Bogy (Mar 23, 2002)

I thought I would see what great words of wisdom some of the rest of you have on a subject I have wondered about for some time. I now have my second Toshiba laptop, and in both cases the instructions have been not to "overcharge" the battery. The easiest when I am at home or in the car is to just plug in the laptop, and then if the power goes out, or I unplug the AC adapter it automatically switches over. When the laptop is at home and plugged in, I often just take the battery out. The only problems is if I decide to take it someplace else in the house and unplug it while it is still on. For all I know this is a problem just with Toshiba and other computers don't carry this warning.

So what is your experience, knowledge, or opinion? Do you plug it in just to charge the battery, and then unplug it as soon as the battery is charged? Do you take the battery out when the computer is plugged in? Do you leave the battery in and just let it charge all the time, letting the battery act as a battery backup?


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## BuckeyeChris (Apr 20, 2004)

I never unplug the AC cord/charger from my Dell Inspiron laptop, unless I use it in a location where either there is no convenient AC outlet, or if I'm just too lazy at the moment to bend down to unplug the charger from my usual location. I also leave the battery in the laptop full time, regardless of whether the laptop is running on the battery or AC. No issues with this since I purchased it new two years ago.


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## AllieVi (Apr 10, 2002)

Bogy said:


> ... I now have my second Toshiba laptop, and in both cases the instructions have been not to "overcharge" the battery. ...


It seems strange that the circuit design wouldn't automatically avoid overcharges.

I have two Dell Inspirons. Neither has ever been unplugged when AC was available and neither battery has ever been removed. I haven't seen problems.


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## Redster (Jan 14, 2004)

We have 20 or so various laptops that our managers use at work / home. The batteries are never removed and the laptop is plugged in if power is conveniently available.


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## Bogy (Mar 23, 2002)

My feeling has always been like Allie, it doesn't make sense to me that the circuitry wouldn't keep the battery from overcharging. My own speculation of a possible problem is that keeping the battery continually plugged in and charging might lessen the capacity of the battery by establishing a "memory", depending on the type of battery. I do occasionally use the laptop on battery only and run it to the "low battery" point and then charge it back up.


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## Cholly (Mar 22, 2004)

Since laptops have lithium ion batteries, there's no real danger of the batteries having a memory characteristic like NiCads have. Could it be that Toshiba has had some instances of batteries overheating or even exploding as a result of being on charge all the time?


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## JM Anthony (Nov 16, 2003)

Include me in the "laptops plugged in all the time, no problems yet" camp. We've got two Inspiron 600m's with no battery problems.


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## Geronimo (Mar 23, 2002)

Well if anything does happen Mainedish and Nick will start posting links proving it is the Mayor and the Governor's fault.

Bogy why are you trying to blame the president for this disater?


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## Bogy (Mar 23, 2002)

Geronimo said:


> Well if anything does happen Mainedish and Nick will start posting links proving it is the Mayor and the Governor's fault.
> 
> Bogy why are you trying to blame the president for this disater?


Hey, the buck has to stop somewhere.


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## Geronimo (Mar 23, 2002)

Well the mayor could have used one of those school buses to evacuatre the battery.


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## Bogy (Mar 23, 2002)

Well, at least the President is all charged up now.


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## TNGTony (Mar 23, 2002)

I have a Toshiba laptop and it is plugged in about 80% of the time. I cycle the battery once a week. But the battery is never removed. No problem so far.

See ya
Tony


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## DonLandis (Dec 17, 2003)

Check the battery type. Laptops have been built with NiCd, NiMh, and Liion type. The best of course is the LiIon type as it can be recharged at any state and never loses full capacity if properly discharged. Plus they are lighter per watt than the others. NiMh are ok and it is said to have "no Memory" which is not true. NiMh are cheap but last only a short shelf life so buying them is not a wise investment. Older technology NiCd do acquire "memory" and must be charged up full, then used to cut off before recharging. Some success has been achieved with sensing circuits to do cut off before the nicd will reverse polarity one or more cells in the series stack. Once you reverse a cell it cannot be fixed without dissecting the battery. Then it is not a good fix. 
I would say that if you want maximum life on your laptop do:

1. NiCd- Use without the battery except when neediong battery power. Use fully until cut off and then recharge fully before use.

2. NiMH Nearly the same as NiCD but these will withstand partial discharge and topping off to full charge but it reduces the number of recharge cycles to half of what you would have gotten if you would have used it like a NiCD. 

3. LiIon Great for no worry use and recharge as needed and leave on the charger all the time if you want.

All battery strings are subject to reverse polarization if operated on a device that discharges the battery fully. 

What happens is a series string of cells discharge evenly in an ideal situation and when the battery reaches a certain voltage the appliance (laptop) shuts it off so the battery doesn't fully discharge, ie it leaves a degree of charge to maintain polarity.

Now if you connect the battery to a resistive load and discharge it fully, what happens in the series is one cell will go to zero before the others in the series string. This will actually put a battery charge of reverse polarity on that cell and begin to charge it in reverse. This ruins the cell and from that point on it will never recovers equally to the rest. You end up with a battery that never charges to full capacity. 

Memory is different. In memory, the battery will charge fully but the discharge current no longer remains flat over time but falls off at a steeper slope. If you make a habit of keeping a charger on the Nicd batteries all the time or don't fully discharge the battery it develops internal resistance build which causes it to lose capacity. In other words, it develops "memory" of a short burn cycle.

One final point about rechargeable batteries, all of them. They have a life that is expressed in recharge cycles. So, recharging them more frequently will reduce their useful life span as you will reach the end of the recharge cycle count. NiCd's are typically 1000 recharges, NiMh are 300-500, and LiIon are said to be 2500. Thus the LiION while it costs much more than the others is actually a better buy over the long haul.

I've written a few articles for rechargeable battery designs for underwater cave diving lights in my time. I've designed and built several high powered underwater cinema lights as well.


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## AllieVi (Apr 10, 2002)

Don,

I learned quite a few things from your post. Thanks for taking the time. :up:


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## DonLandis (Dec 17, 2003)

Thanks- I left out lots of detail but figured that if someone has questions I could post more. I had the privilege of diving with an engineer from the GE battery plant and he enlightened me as to the inner workings of rechargeables and chemistry of how they work. He showed me some tricks to recovering so called dead cells. Also, I was fortunate in getting on his dump list when they made cells that didn't quite meet milspec, I became his dumping ground to use or even resell the cells as I wished.


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## Nick (Apr 23, 2002)

Even my 8 year old electric razor has charge-management circuitry. What's up with Toshiba?


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## Bogy (Mar 23, 2002)

I have a feeling it is one of those CYA type things. I just happen to be the kind of guy who reads through instruction manuals. Don't be too sure that your laptop doesn't say the same thing...somewhere. What it says is that it "may" shorten battery life. Haven't you ever read Dilbert? The people who write instruction manuals aren't necessarily the engineers who design the things. That's why I thought I'd get some opinions from others here.

BTW, thanks Don. My battery is a Lilon, so there shouldn't be a problem.


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## Nick (Apr 23, 2002)

Bogy said:


> I have a feeling it is one of those CYA type things. I just happen to be the kind of guy who reads through instruction manuals.


CYA: "Do not operate toaster while sitting in a bathtub filled with yogurt."


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## CoriBright (May 30, 2002)

Two Toshiba notebooks here, one a 2005 model, connected to A/C about 80% of the time... the other a 2001 model and yes, that one has had two failed batteries in its time. But they don't last forever. It works fine on A/C both with the battery out and with the battery in.

The 2001 Satellite has been 100% A/C for about a year, since it's in the spare bedroom and is used for surfing by guests... and occasionally by me for testing software.

No battery problems with the 2005 A75.


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