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-   -   Testing Batteries With a Multimeter (http://www.diychatroom.com/f18/testing-batteries-multimeter-37566/)

Kent10 02-03-2009 10:54 PM

Testing Batteries With a Multimeter
 
Hi:

I recently bought a multimeter to use with my computer. I also heard that you could test batteries using the multimeter, but that it is not reliable unless the battery is under a load.

I would like to test many types of batteries including button batteries such as CR2025 and CR2032 as well as some smaller battery watches such as a 386, 395 and 377.

I suppose I could buy one of these http://www.ztsinc.com/mbt1.html but they are rather expensive and I already have a multimeter.

What would I need to buy to use the multimeter to test various batteries. I read somewhere that a resistor such as this http://www.radioshack.com/product/in...ductId=2062291
could be used. Would that work? And would I need a different resistor for different batteries. Could I use the same one for all 1.5v batteries, for example.

Thanks so much for any help. Kent

bobelectric 02-04-2009 07:12 AM

When in Doubt, Change Tnem Out.

Kent10 02-04-2009 08:26 AM

Thanks bobelectric. That would work. It is just that I have a couple of kids and a wife who like to mix used batteries and new batteries and so it would be nice to quickly test them. Also I have clocks, for example, that may use up one battery but the other is still good so only one will need to be replaced. And it is kind of fun for us to test the batteries. Thanks.

Pudge565 02-04-2009 08:40 AM

Quote:

Originally Posted by Kent10 (Post 224904)
Thanks bobelectric. That would work. It is just that I have a couple of kids and a wife who like to mix used batteries and new batteries and so it would be nice to quickly test them. Also I have clocks, for example, that may use up one battery but the other is still good so only one will need to be replaced. And it is kind of fun for us to test the batteries. Thanks.

Never use new and old batteries together.

Kent10 02-04-2009 08:44 AM

Is that true even if the older battery is still mostly charged. I have a clock that uses two 386 batteries and when the clock goes weak, one battery seems to be strong while the other is depleted. If I just change the one battery, the clock works very well.

Pudge565 02-04-2009 09:14 AM

I don't know I just follow the directions on the package and that is what they tell me.

bobelectric 02-04-2009 10:00 AM

At least ,change out Smoke Detector batteries, Get recharables for all the gadgets.

KE2KB 02-04-2009 10:13 AM

Here's an inexpensive battery tester sold at your local Radio Shack store.
I have been using their older model for many years, and it's still working.

http://www.radioshack.com/product/in...ductId=2991084

FW

Gigs 02-04-2009 01:18 PM

The problem with using one stronger and one weaker cell in series is that toward the end of the life, the weaker one can get reverse charged and burst.

As an exaggerated example lets say you have one cell at 1.5v and one at 1.0 volts. Then they discharge and one is 0.5 volts and one is 0 volts... now the stronger one will force the weaker one into negative voltage. It's not that simple in real life but that's the idea.

Yoyizit 02-04-2009 02:02 PM

Load a new battery so the voltage drops 10%. Apply this same load to the BUTT (Battery Under TesT). www.hosfelt.com and allelectronics has resistors for this.

Or get a schematic for a battery tester and use those same values and same power ratings.

AllanJ 02-04-2009 02:38 PM

The act of testing under load takes power from the battery and can significantly shorten the life of a small button battery.

If you must test a battery, do it as quickly as possible to reduce the power consumed.

When a battery has questionable strength left, the kind of tester that displays the word "good" or something like that on a little screen will take so long to not display that and much of the remaining power in the battery is consumed.

The size of a resistor for loading depends on the size (in terms of power rating) of the battery. It is definitely not a case of the same value resistor for all 1-1/2 volt batteries etc. Too large a resistance will not perform a meaningful load test on a large battery such as a size D. Too small a resistance will deplete a small button battery in seconds.

Yoyizit 02-04-2009 04:48 PM

The 386 has a 120 mAh capacity. This is the "C" rate.
Usually a battery capacity is measured at the 20 hour rate, which in this case means discharging it with a constant current of 6 mA.

For a watch battery like this to last 30,000 hrs. would take a max. drain of 4uA, but batteries behave strangely at very light loads.

At 1.55v this is a 1/8w load resistor of 258 Ω for a constant resistance discharge. This load shouldn't harm the battery but I don't know how low the voltage should drop for a used battery for a pass/fail judgement. The manufacturers may help you with this. If you e-mail 5 you might get 1 response.

Also, try
http://www.google.com/search?client=...UTF-8&oe=UTF-8
but substitute each battery's techology for "silver oxide".

What you're really testing for is the increase in internal impedance as the battery gets lower in charge, but finding values for this for these types of batteries is like pulling teeth.
A new AA cell has about 0.2 Ω, which means a 1A load would drop the voltage 200 mV.

Please post back with what you find. . .

Kent10 02-04-2009 05:01 PM

This is all very interesting to me. Thanks for all your replies. Gigs: I understand what you are saying about using a stronger and weaker battery together. It probably isn't a good idea. With the alarm clock I mentioned, I wonder if one battery is used for the alarm and the other for the clock because one always gets used up a lot quicker than the other. So except right when I put in 2 new batteries, I think one will always be weaker than the other until one is depleted. I have another wall clock and the same thing happens. One depletes much more quickly than the other so it seems one is always weaker except when 1st installed. Has anyone seen a weak battery burst? I have had leakage from batteries kept in an unused device too long. Is this the same thing? Thanks for your help.

Gigs 02-04-2009 05:04 PM

The open circuit voltage isn't as useless as you guys make out. Yes, it can be misleading, but at the same time, it's still gives a rough approximation for most batteries.

PaliBob 02-04-2009 09:30 PM

Quote:

Originally Posted by Gigs (Post 225164)
The open circuit voltage isn't as useless as you guys make out. .......

I'm with Gigs, if You measure a bunch of batteries of the same type and they mostly measure within a few percent of each other then they are keepers. If any are significantly lower, trash em.


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