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Old 04-19-09, 09:14 AM   #1
Richard Cranium
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Question about quick charger - "top off"

I noticed that after quick charging (2 hour) "AA" or "AAA" batteries in four compartment charger, that if I remove the batteries and reinsert two of the "charged" batteries that the charger will show "charging" again, sometimes for an hour or so.

The charger instructions do say that the left compartment can charge two batteries at a time.

Am I really adding any charge on the second time around, or is the "charge indicator led" just so sensitive that its detecting a minute current so it turns on.

Am I hurting the batteries?
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Old 04-19-09, 10:39 AM   #2
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I'm not an expert on these batteries. But from my experience, there is a point where you can still pump current through them and they don't charge any more. We use some nicads for robots, and the way you tell if they are charged is if they get hot. But they will continue "charging" for hours after that. These batteries self-discharge. The last peak voltage discharges very quickly, and that may be what you are seeing.
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Old 04-19-09, 12:02 PM   #3
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You are cheating the charger and hurting the batteries. The charger has limiting means of determining when to finish charging. When the batteries are charged, the delivered electrical energy turns into heat rather than the chemical energy of a battery. The heat damages the battery. The charger cannot determine right away that the batteries that were reinserted have been already charged up to what was deemed optimal. After you reinsert them, it tries to work with them until it terminates the charging according to some criteria. During that time, virtually no new chemical energy is added while the heat damages the batteries.
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Old 04-19-09, 08:00 PM   #4
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During that time, virtually no new chemical energy is added while the heat damages the batteries.
Thanks, I talked to an engineer who told me about battery analyzers that read the so called "peak voltage." So your answers make perfect sense.

Although, I can't agree that the "heat" is automatic proof of damage to the batteries - it IS proof that that energy is being transferred to the battery and heat is being dissipated. Which of course could mean that no additional charging is being accomplished.

Part of the reason for this question was because I am using a headlight that requires three batteries. This caused me reason to be recharging batteries in different states of discharge.
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Old 04-19-09, 08:38 PM   #5
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Originally Posted by Richard Cranium View Post
Although, I can't agree that the "heat" is automatic proof of damage to the batteries - it IS proof that that energy is being transferred to the battery and heat is being dissipated.
See e.g. the Panasonic site: "The cycle life and other characteristics of batteries are impaired if the batteries are allowed to become too hot during charge." This Duracell page provides you with a quantitative information on how an excessive charge temperature decreases the battery cycle life.
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Old 04-20-09, 07:01 AM   #6
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Funny that the duracell page talks about how heat damages batteries then duracell sells too fast (too hot) chargers.
NiMH chargers don't charge to a certain voltage, they look at a change in voltage while charging so when you plug them back in they start charging until the charger detects the change in voltage.
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Old 04-20-09, 07:30 AM   #7
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Well thanks again, no doubt heat and cold always affect chemical reactions.

But I still wonder, just what mechanisms are used by cheap chargers to detect voltage. I think it's a "dumb" LED with a "current threshold" value needed to light it. Expensive stuff another story......
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Old 04-20-09, 10:58 AM   #8
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Also, on a lot of "quick" chargers although the charge light goes off, they often still apply a very small amount current to the battery. The last time I saw someone test it out, batteries from a quick charger were like 80% charged when the light went out, but if you left them on the charger overnight (even though the charge light was off) they went up to being 100% charged.
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Old 04-20-09, 10:05 PM   #9
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I have an expensive charger, but it doesn't cut off automatically. The radio controlled guys probably know the most about batteries. Unfortunately, I skipped nicads and nimh and went directly to lithium. There is a topping off of lithium batteries, but I'm not sure how that works. But there is a hard voltage cutoff with them, they catch fire if you violate it too badly.
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Old 04-21-09, 08:37 AM   #10
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Originally Posted by Richard Cranium View Post
Well thanks again, no doubt heat and cold always affect chemical reactions.

But I still wonder, just what mechanisms are used by cheap chargers to detect voltage. I think it's a "dumb" LED with a "current threshold" value needed to light it. Expensive stuff another story......
Cheaper chargers its usually the delta V, expensive chargers will be a combination of methods (NiMH assuming here)
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Old 04-22-09, 07:21 PM   #11
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Re-Chargable battery's(charging)..

I've been useing Re-Chargables for almost 8-years..
I have..AA..AAA..C.
I have a 6v..and 2-12volt BATTS..
===
My experiance has been to use my fingers to judge the BATT/tempature..
===
I have a SEARS--FAST Charger..a SEARS..Slow Charger..and RadioSHACK-Charger..
===
I use these batteries for my Digital Still Camera..and I charge them until I feel a good amount of warmth in the CELL-body..
===
When I'm about to do a Photography Project..I need about 3-days to get my AA..fully charged..always allowing the warm touch to say..FULL CHARGE...<<--sometimes over night..
===
I use Nickle Metal-Hydride for my Digital Still Camera's..
My Camcorder's operate useing Li-ION Battery's..
===
My Li-Ion Battery's for the CamCorder Equipment--charge slowly..in a couple of hours..they maintain their CHARGE..for weeks..if I am doing a Project..I just FRESHEN-UP..by letting the CHARGER---work..
===
The Nickle Metal-Hydride Battey's I use are YEARS--OLD..
They give me 100's of Digital Still Photo's..
I really need to charge for 3-days...to get a sufficient Battery...
I usually go 6-Hours each day...on those older battery's...
===
Basically its always the same..I just let em' go until their WARM to the touch..
I have a 12-volt...30-amp Battery I use for Photography LIGHTS..
it can be about 2-days on 6-AMPS of Charge to get that battery WARM...
I'll run that at 4-hour intervals..its a AGM Battery...(wheel chair battery)..
Other's just use SMART Charger's that just SHUT-OFF..//..you, learn how good your portable power actually is..and adjust..
===
You can even do---20-minutes...for days...I recharge my CELL Phone that way...
===
HEAT is the enemy of a Battery..
But WARM---ain't...
===
Also useing your BATTS...in a cold environment..are a bad thing..
===
Store the Battery's in a warm place...room tempature...
===
Use your SENSE-of-TOUCH...a warm battery is a happy battery.
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Old 04-23-09, 01:26 AM   #12
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Quote:
Originally Posted by 24X18 View Post
I've been useing Re-Chargables for almost 8-years..
I have..AA..AAA..C.
I have a 6v..and 2-12volt BATTS..
===
My experiance has been to use my fingers to judge the BATT/tempature..
===
I have a SEARS--FAST Charger..a SEARS..Slow Charger..and RadioSHACK-Charger..
===
I use these batteries for my Digital Still Camera..and I charge them until I feel a good amount of warmth in the CELL-body..
===
When I'm about to do a Photography Project..I need about 3-days to get my AA..fully charged..always allowing the warm touch to say..FULL CHARGE...<<--sometimes over night..
===
I use Nickle Metal-Hydride for my Digital Still Camera's..
My Camcorder's operate useing Li-ION Battery's..
===
My Li-Ion Battery's for the CamCorder Equipment--charge slowly..in a couple of hours..they maintain their CHARGE..for weeks..if I am doing a Project..I just FRESHEN-UP..by letting the CHARGER---work..
===
The Nickle Metal-Hydride Battey's I use are YEARS--OLD..
They give me 100's of Digital Still Photo's..
I really need to charge for 3-days...to get a sufficient Battery...
I usually go 6-Hours each day...on those older battery's...
===
Basically its always the same..I just let em' go until their WARM to the touch..
I have a 12-volt...30-amp Battery I use for Photography LIGHTS..
it can be about 2-days on 6-AMPS of Charge to get that battery WARM...
I'll run that at 4-hour intervals..its a AGM Battery...(wheel chair battery)..
Other's just use SMART Charger's that just SHUT-OFF..//..you, learn how good your portable power actually is..and adjust..
===
You can even do---20-minutes...for days...I recharge my CELL Phone that way...
===
HEAT is the enemy of a Battery..
But WARM---ain't...
===
Also useing your BATTS...in a cold environment..are a bad thing..
===
Store the Battery's in a warm place...room tempature...
===
Use your SENSE-of-TOUCH...a warm battery is a happy battery.
A warm battery is often a battery that is trying to dissipate overcharge and again is often being damaged in the process.

You really should either stop using batteries or buy a decent charger.
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Old 04-24-09, 08:24 AM   #13
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you also can;t tell by heat, a battery that feels warm to the touch could be too hot internally and you would never know it.
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Old 04-27-09, 02:35 AM   #14
24X18
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Recharging batteries-nervously/

The matter is really quite simple..batteries are very old technology..
Useing a Battery Charger has differant modes applied in the retail purchase..
I think that a simple TIMER is applied where it can fit the package..other than that..for a Voltage-limiter..
Larger than the STATED Voltage are used in a Battery Charger--if your charging 12-volts..you can in alot of good Battery Charger's be useing 15-volts..Automobiles can use upwards to 18-volts to charge the 12-volt Deep Cycle battery..
..Batteries are all about a STANDING CHARGE--
..this is really your measuring stick for a quality purchase..
..being Nervous Nelly--about technology really looses alot in the pleasure of having these products..
..if you think for a moment..doesn't a TIMER actually solve the matter--considering your Seller package might state--USE THE Supplied Charger ONLY..this would allow for a simple-answer..NOT..that we need to LOOP-de-LOOPS..
Other than that..having a Process to determine that your Battery is being CHARGED--PER-Polarity..suffices also..
Its best NOT to turn RETAIL--into a circus.

Last edited by 24X18; 04-27-09 at 02:36 AM. Reason: SP
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