Is a battery's initial voltage a good measure of life expectancy?

sandermarijn · Jun 18, 2012

I have some 2CR5 batteries dated 2008, as well as some newer ones (2020). All are unused. The older batteries have an open-circuit voltage of 7.06 V, the 2020 batteries are 7.08 V.

Is the measured voltage a reliable measure of life span? IOW, can I rely on these older batteries?

In a related question: how accurate are the expiry dates of lithium batteries? Like with a pack of salt or more like with milk?

Thanks guys (and the occasional girl),
Sander

tkamiya · Jun 18, 2012

No, it's not.

What is called an "Open Voltage" - a measure of voltage when there is no load attached to it, is usually right at the specification. By the time that drops lower, it's seriously degraded.

What's important is the voltage under load. Many battery checker uses small register as a simulated load, then measure the voltage.

I'm guessing you used digital multi-meter. If that's the case, unless it has a special battery check mode, you are measuring an open voltage. Plus, the accuracy of many meters like that are so that .02 volt difference is within the margin of error.

Steve Smith · Jun 18, 2012

sandermarijn said:
In a related question: how accurate are the expiry dates of lithium batteries?

The voltage isn't suddenly going to drop to zero at one minute past midnight on the expiry date.

If they measure close to seven volts open circuit, I would consider them as good as new and use them without worrying about them.

Steve.

sandermarijn · Jun 18, 2012

tkamiya said:
What is called an "Open Voltage" - a measure of voltage when there is no load attached to it, is usually right at the specification. By the time that drops lower, it's seriously degraded.

Sounds good .

tkamiya said:
I'm guessing you used digital multi-meter. If that's the case, unless it has a special battery check mode, you are measuring an open voltage. Plus, the accuracy of many meters like that are so that .02 volt difference is within the margin of error.

Yes, cheapy digital multimeter. No battery check mode on those, maybe I should get a real one. Of course my EOS does have a built-in battery meter, but that one isn't very accurate I suppose ("OK, almost dead, dead").

I wonder, does the open-circuit voltage ever drop, also long after the expiry date has passed? IOW, is there a situation thinkable wherein the open voltage does represent a faithful indication of life left? How long past expiry will it typically take a lithium battery to show such significant open voltage degrading?

sandermarijn · Jun 18, 2012

Steve Smith said:
The voltage isn't suddenly going to drop to zero at one minute past midnight on the expiry date.

Happened to me with a pack of salt the other day .

Leigh B · Jun 18, 2012

dupe

How the heck do you delete a post???

Leigh B · Jun 18, 2012

Most modern battery technologies hold nominal voltage pretty closely until end-of-life. That's true both under load and open-circuit.

Common zinc-carbon batteries like D-cells in flashlights, are an exception. The voltage drops uniformly during use, and end-of-life is application-dependent.

Your 2008 batteries are probably still usable, but don't put them in a pacemaker.

- Leigh

sandermarijn · Jun 18, 2012

Leigh B said:
Your 2008 batteries are probably still usable, but don't put them in a pacemaker.

Or in a space shuttle.

vedmak · Jun 18, 2012

just hock it up to some load(optimally similar to one they will be used with) and monitor voltage for 10 min or so if it is not good you will see right away.

polyglot · Jun 18, 2012

The other thing is that since it's a lithium, the discharge curve is pretty flat, i.e. the voltage doesn't vary much during the normal life of the battery. Once it's exhausted, the voltage drops off quite precipitously.

Another vote for "probably fine just don't trust them much".

CJBo001 · Jun 18, 2012

battery testing

tkyama is correct; it is voltage under load that tells you the condition.

electrical engineer's explanation (optional):
The simplest model for a battery is an emf (from the chemical process) in series with a resistance. As the battery fails the emf stays the same but the resistance increases. Hence as you draw current the voltage observed at the terminals of an exhausted battery will be less than that which will be produced by a good battery because of voltage drop across the internal resistance.

quick and dirty test of battery condition:
If your multimeter has a 10 amp dc range (be sure you plug the leads into the right places!!) connect it briefly (emphasis on briefly) across the the battery terminals and measure the short circuit current. The difference between a good battery and an exhausted one will be quite apparent.

Chuck

sandermarijn · Jun 18, 2012

CJBo001 said:
tkyama is correct; it is voltage under load that tells you the condition.

electrical engineer's explanation (optional):
The simplest model for a battery is an emf (from the chemical process) in series with a resistance. As the battery fails the emf stays the same but the resistance increases. Hence as you draw current the voltage observed at the terminals of an exhausted battery will be less than that which will be produced by a good battery because of voltage drop across the internal resistance.

quick and dirty test of battery condition:
If your multimeter has a 10 amp dc range (be sure you plug the leads into the right places!!) connect it briefly (emphasis on briefly) across the the battery terminals and measure the short circuit current. The difference between a good battery and an exhausted one will be quite apparent.

Chuck

Thanks Chuck, that's very helpful. Just don't talk too much about the European Monetary Fund- way too far up my throat already .

I'll try your suggestion of shorting the terminals and measuring the current. I will need to get a better multimeter first (need a proper one anyway).

I assume that a good battery will show a constant (within limits) short circuit current, while the bad battery's current will drop quickly and sharply?

Hm, better not do this experiment with every 2CR5 I have, they're kind of expensive.

sandermarijn · Jun 18, 2012

vedmak said:
just hock it up to some load(optimally similar to one they will be used with) and monitor voltage for 10 min or so if it is not good you will see right away.

Good plan, will have to get some wiring and think of a good load (yeah, the camera will do).

Alternatively, a multimeter with dedicated battery testing mode will do the exact same thing if left to run for the same duration, no?

Leigh B · Jun 19, 2012

CJBo001 said:
If your multimeter has a 10 amp dc range (be sure you plug the leads into the right places!!) connect it briefly (emphasis on briefly) across the the battery terminals and measure the short circuit current.

That's a good way to blow up the battery.

I would never try that, even though I have the proper equipment and know how to use it.

Regarding test methodologies for lithium cells... There are no accurate tests that will give battery condition.

- Leigh

Nicholas Lindan · Jun 19, 2012

I have equipment with lithium batteries that were installed in 1988 - still going 'strong'. These were used to back-up CMOS non-volatile memory in the days before flash memory and the drain on the battery was close to zero for these past 24 years.

If they are Panasonic batteries then I wouldn't worry about the expiry date until it is 20 years past. If they are Eveready or Mallory then I would be wary.

sandermarijn · Jun 19, 2012

The old ones are Philips, the newer are Panasonic. Both respectable enough brands I figure.

sandermarijn · Jun 19, 2012

Leigh B said:
Regarding test methodologies for lithium cells... There are no accurate tests that will give battery condition.

I'll just use the batteries and see how long they last. Can't think of a better test.

lxdude · Jun 19, 2012

Just what I was going to suggest. Put in old ones and carry spares. If you only got half the life you'd still be doing OK.

BobD · Jun 19, 2012

I have always tested non-rechargeable batteries (old and new) for years and years by simply measuring the voltage. Techies always say this is wrong and "it won't tell you the state of the battery under load" blah blah blah but, for me, measuring the voltage has always worked fine and batteries that test at or near spec voltage have always worked fine and those that don't have always not worked fine.

However, I wouldn't rely on this method for testing used rechargeable batteries or the battery of a car, boat or aircraft I was about to climb aboard for a trip.

Is a battery's initial voltage a good measure of life expectancy?

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