Not an alert, but a notice

[vadimax]

Once upon a time I have purchased several Fujitsu NiMH AA cells. They are claimed to be HR-3UA, min. 2500 mAh capable, manufactured by FDK Corporation in Japan. Everything sounds good, right?

But at least one of them has "lost" its upper limit and an ability to store power: you may charge it indefinitely. Right now I have pulled this one out of Xtar VC4 charger while there was an indication of 3200+ mAh charged. It was noticeably warm, not even close to "hot". At the same time lights I used to put it in refused to operate very quickly. First I was inclined to blame the lights for their poorly made drivers with high parasitic drain, but then understood that this cannot be the reason — they are of different manufacturers and turned out to be OK with different other cells.

Is this enough to avoid this brand?

P.S.: An after all this super-puper overcharging Zebralight SC53Fc blinks only once, indicating that the cell is close to discharged state.

P.P.S.: Yeah, I know — I must find and check other Fujitsu cells. One is not a rule

 

[sbj]

At first I would blame the charger or an incorrect setting for overcharging a NiMh battery.

Did you charge with 0.5 or 1.0A? As NiMh batteries age, the chargers have a harder time recognizing the delta peak correctly.

At the moment I only have 2 Fujitsu AA batteries in constant use. So far these behave just as reliably as the black eneloops.

 

[Lynx_Arc]

First off how many charge cycles have you put these batteries through and second how many mah have they normally charged to. If these are old 2500 cells made in Japan then they could be the same crappy ones that Energizer sold long ago that after so many cycles went to very high self discharge often going to nothing in capacity in but a few days and with lower capacity also. Almost everyone I know that has had these 2500mah Japan cells has trashed them as they just go bad and frustrate you till you figure out what is going on. To add insult to injury they had a 4 channel super fast charger back then (15 minute Energizer charger). This charger accelerated the demise of the 2500 cells even more.

Edit: I just remembered that some of these very high capacity nimh cells have a problem with developing high internal resistance which can affect charging and also can greatly reduce power output under heavy loads. Older nimh cells over time lose capacity by use and recharging plus damaged ones can lose considerable capacity 1/3 to 1/2 or more and cells in series if overdischarged and even reverse charged can be greatly damaged. All of these lead to a cell that has 2500 mah ending up only having 500mah and high internal resistance such that a charger never completes charging and they seem to die quickly. If you have one weak cell with one good one then the weak one will be discharged in use in series and unable to hold voltage under a load at all.

I would do a capacity test on both cells and also test voltage off the charger, let them rest and check them daily for a week or two and compare voltage drops on both. A cell with high internal resistance should keep dropping in voltage below 1.3v in a short while while good ones should be 1.33v or more (eneloops) after several weeks.

 

[bykfixer]

Sometimes a battery stops working. Doesn't mean they'll all stop suddenly.
S'not a big deal.