# are my batteries overcharged at 1.4?



## Minni

Hi, I'd gotten a Duracell Value Charger a few years ago, then this week needed to recharge the *2000 MAH*, NiMH batteries which came with the charger. I had them plugged into the charger throughout the night, approx. 12 or 14 hours.

Next day, when i checked them via multimeter:
their readings were approx. 1.4

Is that bad for their longevity? (are they too overcharged?
Forget about attempting Duracell support - they're like :banghead:
:rilleyes:


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## WereBo

Hi Minni :wave:

There's no problem with 'overcharging' batteries, once they're 'filled' they just stay topped up until needed. The only problem might be if they're left charging for weeks on end, then you might notice a slight rise in your electric-bill :wink:

Some rechargeable batteries can suffer what's called 'battery memory' (mainly Nickel-based batteries) where they gradually lose their maximum energy capacity, if they are repeatedly recharged after being only partially discharged.


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## sinclair_tm

What kind of batteries are you charging? If it's AA or AAA, they are 1.5V batteries, so 1.4V is under charged.


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## Done_Fishin

With all respect to my fellow members 

rechargeable batteries should never be overcharged nor left on charge for longer than the required time to recharge

1.4 Volts is fine for a fully charged rechargeable battery NiMH or NiCd .. if the voltage during charging exceeds 1.42 V then there is every possibility that the battery has been damaged or will be damaged should charging at this voltage continue. Overcharging the batteries either time-wise or voltage-wise will tend to boil the battery dry. should the battery exhibit a higher charging voltage than the 1.42Volts then most likely the battery has suffered an increase in internal resistance which will cause voltage loss and current reduction when in use.

Batteries that are kept in long term storage unused may fail unexpectedly either during use or during recharge. They are usually kept in best condition by charge - discharge cycling about once a month ..


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## Minni

Done Fishin' thanks so much - btw, i'm opposite of you - not quite yet age impaired, yet virtually old, 
...and so I quite understand how batteries need to "gently" be charged/discharged, and how they're at risk of boiling dry (what computers do to my EMF-sensitive anatomy)

Unfortunately, with my Non-Smart value charger causing the risk of "abusing" my poor batteries (I.E. if during some recharge cycle they wind up charged, say, in the High 140s, is there any *best* way to discharge them - to maintain longevity?


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## WereBo

The easiest way is to put 'em in a torch or something, leave it on 'til the light goes out, then leave it for an extra 30 minutes or so. They should be fully discharged and ready for re-charging then - Rechargeable batteries need to be 'gently' discharged rather than rapidly, to help maintain longevity.


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## Done_Fishin

there are specific limits to the discharge levels of rechargeable batteries that one should never go beyond .. I seem to remember that Ni Cd should never be allowed to go below 0.5V per cell and definitely no battery should ever be allowed to totally discharge towards 0V (zero volts). Some may never recover. in fact some of the newer types of battery if discharged to too low a voltage will trip a controller circuit and they will not charge again without being placed on a special circuit and then sometimes that discharge cycle they went through makes them totally useless.

I tend to look for the manufacturers recommendations for the batteries in question .. see what they recommend and then work from there .. it's also one of the reasons why Smart Chargers became popular since there are so many things to consider when charging batteries (amongst others Heat, Cell Voltage & Charging Current) that if not observed will quickly degrade the battery and its usefulness. A "GOOD" smart charger monitors all the vital details and changes the charging routine when any of the programmed conditions is violated. 

think about your cell phone . when the battery voltage drops below a minimum it closes down. you place it on charge regardless of the condition of the battery and it charges just enough to bring it back up to peak condition, then stops. Refusing to charge any more until it has discharged to a certain level. 

To do the same without recourse to a smart charger would require sitting by the batteries with a thermometer, a charger & and a Voltmeter ensuring that the charging current (either pulsed or dc) is at the rated value, the cell voltage hasn't exceeded the maximum value and the cell temperature is within specifications. 

The same applies to discharging of course except that the battery shouldn't go below specific level!

I suggest a read here 

Nickel

where, amongst other things, they state that 



> Discharging
> 
> A fully charged cell supplies an average 1.25 V/cell during discharge, down to about 1.0–1.1 V/cell (further discharge may cause permanent damage in the case of multi-cell packs, due to polarity reversal). Under a light load (0.5 ampere), the starting voltage of a freshly charged AA NiMH cell in good condition is about 1.4 volts.[18]



Personally I would go with the method that werebo says, by discharging through a filament bulb, except that I would stop the discharge when the bub still has a feeble glow. You'd need to calculate though for 1Volt per cell and obviously you'd need 2 cells for a 2,5V bulb, 3 cells for a 3,6V bulb etc .. and keep the bulb wattage to a reasonable discharge rate for the cells being used so that you don't draw so much current that the cells overheat.


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## Minni

OK, I see. Thanks. BTW, I seem to recall an Ehow (or other) article advising people to increase NiCd longevity by FULLY discharging them, then waiting a few minutes, then recharging them.

The article is probably findable via precise keywords via Ixquick or Google


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