In my never-ending quest to become as geekily informed as possible - I borrowed a digital voltmeter to test batteries after charging. I did this because I was unpleasantly surprised to discover my new 2600mA duracells appeared to "suck" (slang term for failed to hold charge)

I checked a number of Energizer cells, both double and triple A and they read 1.35 volts for over a week after charging. The new Duracells read 1.46 - immediately after charging, but have fallen to 1.32 48 hours after a 20 hour trickle charge.

My question : Does an "unloaded" voltage check of a battery's status predict it's effectiveness of service life?
In other words, now that the Duracells have fallen to 1.32 volts, eve before using, does this mean they will fail before another battery reading 1.40 volts?

Is there a more realistic "cutoff" for an unloaded battery test? Are all batteries fine as long as they read above 1.25 when unloaded?

Your geeky but accurate replies are requested. The more technical the better.

I don't believe from all I have read about batteries that cell voltage is a good indicator of anything but cell voltage. Would be super nice if voltage alone would be a good predictor of charge, battery condition, service life or anything besides 'voltage'. I would like to see some data collected to determine if the voltage correlates with anything. Sure would make life easier. But from what I think I know the best indicator is battery energy or watt-hours. That means amps x volts x time to charge (input watt-hours) and same for output watt-hours. That becomes much more complicated to measure though some of the chargers do measure mAh which is close but doesnt take into account the cell voltage.

In what kind of device are you using the Duracells? I've noticed that mine seem to do great in my moderate-draw GPSs and have better run times than any other cells I've used. But they aren't at all good in my digital camera when compared to other NiMH cells.
It would be nice if a quick test of open-circuit voltage were a valid measure of the cell's state of charge but I don't think it's indicative of anything useful except to show that the cell isn't completely discharged.

Well, I ran the light while riding last night for an hour. Don't know what kind of current or "watts" were being used. I checked the cells after the ride and they had dropped from 1.32 to an average of 1.27.

The reason for this inquiry was the "surprise failure" of the duracells after they had sat around for a week. My other energizer cells, and radio shack cells had been charged at the same time were still working.

It just "dawned" on me that the reading at the battery case terminals was 5.2 volts, now I wonder if I can rig a connection to read the current and or voltage while the light is on as well......

You need a lot to accuratly measure the batterie's voltage. A simple ressitor across it then measure the voltage would do, thats all battery monitors do, just with a really accurate resistance across it.

Until I started buying the Eneloops and some of the long storage Ray o vacs, my energizers would just lose their charge in about a week. They didn't seem to hold or maintain there charge for very long. The Eneloops will hold their charge for months and the RayOVacs at least as long. The Eneloops are called low static discharge and the RayOVac is called a hybrid rechargeable battery. These batteries are almost perfect. The duracells are I believe are called precharged and will hold their charge for up to a year.

torgrot

The correct term for both the Sanyo's and RayoVac's is Low Self Discharge. The names eneloop and hybrid are just the marketing names.

About the only thing you can say for certain is that if the cell voltage is around 1.0V the runtime will be very low.

https://www.users.on.net/~mhains/Reviews.html Seems to be the best source of info on Nmhy batteries.
Another tester felt that the big two battery makers were more interested in their other batteries than the re-chargables.

I bought some Duracell NIMH as well...they hold a charge, not at all...if I charge them and put them in my light or camera I get the advertised runtime or number of photos...if I let them sit for a week, I get nothing.

Duracell has both old fashioned NiMH and low self discharge. Their Low self discharge is called pre-charged and if you look at the top and its white its the same as an eneloop, duraloops is the street name for them now, a black top comes from the other factory along with the rayovac's and others.

+1 that's pretty much the results I get from all the Nimh I've tried.

I ran the Duracells for a second time - last night for another 40 or 50 minutes. So I am satisifed they are not damaged or defective. And with this "test ride" the cells have been charged for over 72 hours so I guess I can trust them for most conceivable situations.

The only thing I have noticed is that one "pair" of the cells started off at a fraction of a lower charge, and those two cells continue to discharge ahead of the other two cells that were all charged at the same time time in a 4 bay trickle charger......

After over three days from charging - and after nearly two hours of run time, I now have two cells at 1.23 and two cells at 1.29.........good enough for any of my situations....

72 hours? Trickle charger? That could be part of the issue. NiMH are not as tolerant with trickle charging as NiCad, they can tolerate trickle charging if the charge current is really low but trickle charging is one way to reduce their lifespan.
Get a decent charger, Maha, lacross, etc and you will get better life.

Interesting topic, how do laptops know how much juice is left in a battery? I would guess they measure the voltage drop and compare with the voltage fully charged.

I think they estimate power consumed and deduct it from the assumed mAh of the battery, I think most modern laptops have a 'powermeter' that is capable of being calibrated.

Also, laptops don't generally use Nimh any more, lithium based cells have different voltage drop as they discharge and when discharged relatively slowly (as in a laptop) the voltage could stay level for most of the run time.

NiMH cells and Lithium cells have very similar discharge curves, i.e. a near linear voltage to capacity remaining figure once the initial peak has been discharged and before the rapid reduction at near depletion. You can predict the remaining capacity for either cell type (and for NiCd) under load.

However, it must be noted that the voltage is also dependant on the load applied so must be deduced for that cell and load combination.

If you want to know available capacity, spring for the $50 and get a Maha c-900 charger. When I did, I found that my 20+ used Energizer 2500mah NiHms averaged less than 1500 available mah. Upon further research at CPF, it turns out that they have a horrible reputation for longevity and self discharge. So, I trashed almost all of them after reviving a few of them with the Maha's break in and cycle routines.

The high dollar 2000 Mah LSD batteries are great for applications where the battery is sitting around for months at a time. But the $/mah ratio is too high for bike lights that get used all the time. Get a good charger and good quality batteries and visit "Battery University" at CPF. Check out the Maha too. It'll give you an education.

There is, apparently, a potential problem with all AA cells with a capacity over 2000 mAh. It is related to the plate thickness being too thin which causes early failures especially when used at reasonable currents. For AA cells, the recommendation is to use cells of no more than 2000 mAh if you want them to last.

I too use duracell 2650's and found them to be great cells.. what charger are you using??

The only other battery that is comparable in quality is the Titanium 2700's, they cost a little more than the duracells..

https://www.batteryjunction.com/tpeh-taa2700.html

I use the Vanson charger, will charge just about all cell types.. aa, aaa, c, d and 9 volt

https://www.batteryjunction.com/vabcunsmch.html

Again, most of my comments are a limited to the 24 batteries I've played with.

My comments about duracell 2600s were from a "one time" occurrence after a quick charging. They actually worked fairly well after a trickle charge.

But the latest "quirk" discovered in testing the 4 duracells is the uneven discharge rate. Two of the cells continue to act as if they are some how less chargeable, and therefor discharge to a greater extent when mated the other pair.

My only guess is that I damaged two of the batteries - or somehow the chargers do not charge both pair evenly......

I did discover that an unloaded cell can still report 1.15 volts but not be on average = strong enough to run my Stella "double eh"--- blinks outs almost immediately.......

And like I said, I have no experience, so far all my batteries have less than 5 cycles of usage.... my own concern is to be carrying the right amount for any given overnight ride.....

What charger? Quick charging is hard on batteries as well as pair charging.