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

1. ## 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

2. Originally Posted by CJBo001
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.

3. Originally Posted by vedmak
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?

4. Originally Posted by CJBo001
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

5. 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.

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

7. Originally Posted by Leigh B
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.

8. 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.

9. 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.

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