# Leaving a battery in the charger



## richgreer (Dec 25, 2009)

I have extra batteries for all the cordless tools I own. The extras are usually in the charger and I swap them whenever the battery I am using runs low. I think that is a fairly common practice.

Sometimes, a battery can remain in the charger for a few weeks before I swap it out. Does that do any harm to the batter or the charger?

If it is relevant, most of my cordless tools are DeWalt with 18 volt batteries.


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## JoeLyddon (Apr 22, 2007)

I think it would depend on how "smart" the charger was…

If it turns-off when the battery has been charged, you're probably safe.

BUT…

If the charger just keeps on charging, you will be reducing the life of your batteries.

I tend to remove them from the charger when they're charged… Then, I don't have to worry about it. LOL


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## idunno (Mar 30, 2011)

There's some potential of reducing the lifespan of the batteries-they tend to be happier being stored at less than maximum charge. Also, even if the if the charger is smart, won't it end up "topping off" the battery every time the charge dissipates a little bit? That frequent charging could have some effect.

There's probably nothing major wrong with leaving the batteries on the charger… but I'm a little paranoid about charging batteries, and the potential for overheating and fire. So I try to only have batteries on the charger while I'm around, and able to take action if anything goes wrong.


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## JonathanG (Jan 18, 2010)

Rich,

I received a DeWalt 18v cordless drill for Christmas and it came with 2-batteries. I seem to remember the manual saying to leave one in the charger and plugged-in, but I'll have to check when I get home from work and post back.


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## Woodwrecker (Aug 11, 2008)

I have the same as you Rich.
And I leave the extra's in there.
It doesn't seem to affect them at all, and I use my drills a lot.


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## patron (Apr 2, 2009)

same here rich

only my older
earlier batts and chargers
(makita)
would discharge or over charge

the new ones all have 'smarts'
seem to do just fine
left alone

then i know they are charged and not dead
(i take tools to jobs
and they don't get plugged in sometimes)


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## jbertelson (Sep 26, 2009)

Definitely unique to the charger and perhaps the battery type. I usually am lazy, and there is a battery in the charger….....besides, it keeps the dust out of the charger…..........(-:


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## Grandpa (Jan 28, 2011)

Dewalt chargers are supposed to have a topping off feature that does not harm them. The owner's manual and also some magazine articles I have read tell you it is okay (actually preferred) to keep them on the charger all the time. The most important thing is to change the battery to a fresh one at the first sign of the battery being low. If the battery is totally discharged one of the cells can get reversed polarity and then it fights the others when you charge it. My brother-in-law is an engineer with a masters degree and he is also from the old school of "totally discharge the battery so you don't have a memory develop". I can't get him to read the manual though. He goes through drills and batteries faster than I can change sox. Those days are supposed to be gone and the main thing is to keep them on the charger and never totally discharge them. Also the repair center in Oklahoma city told me that the battery is designed to last 5 years. I am still not sure how you build a timer into the battery but the man said if it is getting close to 5 years you might want to think about having the drill motor rebuilt because the batteries cost as much as a new drill mother with batteries included. That is what I have read so take it for what it is worth.


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## doughan (Apr 22, 2011)

You could always break down ,burn your man card and read the instructions.


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## Loren (May 30, 2008)

I don't leave them in for longer than 18 hours or so. I think it's bad
policy to leave them on.

I have my chargers plugged into a power strip. I turn the strip on
when I want the chargers to be active. I turn the strip off when
I don't. Chargers will draw electricity if left on anyway, so using 
a strip saves a bit of electricity.

The older chargers used to "cook" batteries. More hi-tech chargers
often have a quick charge mode which will get your battery up to
working in a short time. Some will also do a deep charge of 12 hours
or more. I try to run them overnight to get the deep charge.

When the batteries get real knackered it doesn't seem to matter,
they just suck anyway you do it. But batteries in good condition can
be messed up by leaving them on the charger because they drop 
about 3% of the charge per day - which will make the charger pop
on and top them off frequently. Whether they develop "memory" 
or not and whether it can be erased is open to debate, but I'd rather
play safe than sorry.

I know how to "surge charge" a battery by hitting it with double it's
rated voltage for a few seconds. The method is sometimes called 
"the nicad battery fix". My results with it have been fitful. Pretty
much, when they go they go - even though you can nurse them
along for awhile at a poor level of performance by surge charging them.

The lithium batteries are different. I'm still using Ni-cads.


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## Dark_Lightning (Nov 20, 2009)

Interesting article at Wiki about battery memory. Essentially, we will never replicate these conditions on earth.

http://en.wikipedia.org/wiki/Nickel-cadmium_battery#Memory_and_lazy_battery_effects

I've left my Makita batteries in the charger for days, with no ill effects. Maybe I have a "smart" one… but it's over 15 years old. Oh, yeah, 15 year-olds know it all. Never mind.

Note- you are wasting electricity with this practice, though. How much, I dunno.


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## kpo101 (Mar 15, 2011)

I've used just about all types and brands of battery tools knowned. And i have a friend in the Dewalt line that will say from engineers in the field that leaving a battery in the charger for a total of 20 minutes after its charged will start a decline in its charge life. He also said that the only way to completely charge a ni-cad battery is to run it completely dead. Oh and all Ni-Cad batteries have a memory.So i say to use them, put them on charge and when u finish your project gather all your batteries and charge them the right way. i have some Dewalt batteries that are 13 years old.


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## Greedo (Apr 18, 2010)

the absolute best and safest method is to remove the battery from the charger inmediately after it is charged, and unplug the charger.
leaving the battery in an unplugged charger wil slowly drain the battery, even with new ones. leaving it in a plugged charger will also drain it, and then recharge it. wearing it out for nothing.
my festool drill manual mentions that you must remove the battery from the charger once charged.


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## Grandpa (Jan 28, 2011)

My Rigid manual say to store the battery without a full charge. this charger gives a full charge in 20 minutes. My Dewalt drills both say to leave the battery in the charge. I have read this from magazines also but hey I am not an EE.


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## JoeLyddon (Apr 22, 2007)

It all depends on how "smart" the chargers are…

Those that disconnect the charging circuit when battery reaches Full charge are the best!
(most of the high class charges do this… BUT, if you don't know, that is where it makes a difference)


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