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What causes a rechargeable AA battery to go "high"?


stacysound

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I’m going through all of my rechargeable AA batteries and have run across a couple that will show to be “high”. I’m using the powerex MH-C9000 for analysis. Sure enough when I measure the voltage across the battery it’s 2.24v. I discharged the battery and reconditioned it and it seems to work fine. 

But, I’m curious at what would make a battery go high?

Stay safe.

IMG_9567.jpeg

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To Stacey: I have never seen this. What are you using to measure the voltage? 

 

To Jason: As far as I know there is only one electrolyte in the battery and it's on both sides of the membrane. The membrane prevents the anode and cathode from touching and shorting out. It also prevents dendrites from growing, touching and bleeding current from the anode to cathode, slowly draining the battery in less than a day. 

 

I do know that the battery voltage can go up due to gas (oxygen) pressure build up in the battery and this will temporarily raise the voltage. Any kind of load will drop the voltage quickly as the over pressure is dropped. I've not seen numbers like 2.24 Volts. Never to late to learn though.

Best Regards,

Larry Fisher

 

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I'll take a picture of it if it happens again. The "charger" stops it's analysis of the battery and displays "high" and the voltage. Mine was 2.2 in the charger. I measured it with a Fluke volt meter and got 2.24v. 

 

I'll double check myself on the next cycle.

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Here's a chart I found on line. The right half of the chart is charging a fully charged battery, i.e., the battery is being overcharged. The voltage drops because the battery begins excesoxygen recombines producing heat. Most fast chargers look for the voltage dip to know when to terminate the charge.

Eneloop AA HR-3UTGB 1900mAh (White)-Charge.png

Having two meters read the same is pretty definitive and Fluke meters aren't known for being incorrect.  2.24 Volts could make some devices unhappy. Did the voltage drop to normal after an hour or so of rest?

 LEF

As Jason suggested maybe something is "broken" in the battery.

LEF

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Like I said, probably misremembered from something else.

I found this in the manual -

 

To ensure safety, the charger performs a battery health “impedance 
check” at the beginning of the program. If the battery fails this test, 
“HIGH” would be displayed and program will be terminated.

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I have the same charger and after a while, some batteries give me the HIGH warning too. They seem to be garbage after that.

 

My first batch of Powerex 2700 batteries all pretty much did this eventually. The Eneloop ones I have now I haven't seen any show me the error yet. 

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I've seized the opportunity to test, recondition, and sort my Black Eneloop Pro and Powerex Imedion rechargeable AAs.

 

The black Eneloop Pros are about five years old and have been used on a fairly regular basis. So far I've reconditioned 68 of my cache of 72. They are showing excellent results as over half of them report better than 99% of their rating of 2450mAh and more than 90% of them show better than 97% of their rating. Two of the 68 reported "HIGH." After reading the above posts I checked several of my reconditioned ones and they showed an open circuit voltage of 2.5 to 2.7v, so that range appears to be normal. Again, this is an "open circuit" test (no load).

 

My supply of six year old Imedion rechargeables are now undergoing the procedure.

 

I've been at this for more than a couple of weeks now as the Maha Powerex MH-C9000 unit takes over thirteen hours to cycle a set of four in REFRESH/ANALYZE mode at my chosen settings.

 

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I have seen this with two of my oldest eneloop pro (Panasonic branded). They are definitely over 5 years old.

My conclusion is that they are dead at this point. I have just like JB taken the time to run the condition/analyze cycle during this downtime. With those two batteries set to charge the powerex charger says HIGH, but voltage shows about 1.2v and it will not agree to run the discharge cycle.

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