Members UMT Posted March 29, 2009 Members Share Posted March 29, 2009 I've got a battery tester that tests all sorts of batteries. The other day, I needed my mini flashlite to work so I pulled the 2 AA batteries and the 'tester' says they are fine. I get to my project and it is pitch black dark and the batteries fail in about 3 minutes! AAAAAAaaaaererrgh! I've had this happen more than once! So tell me, does anyone make or can I make my own battery tester that actually WORKS? (I'm not interested in spending wads of hard earned cash either!) Thanks!UMT Link to comment Share on other sites More sharing options...
Members mike42 Posted March 29, 2009 Members Share Posted March 29, 2009 The problem is that no one knows exactly what load (the amount of work ) you're going to expect the battery to handle. Every electrical device puts a different load on a battery than any other device does. So most "testers" either use a "no load" test condition, or some arbitrary fixed load that the tester mfgr just pulls out of the air. Someone may make some fairly sophisticated tester with selectable loads, but if so, it's probably pretty expensive. Best suggestion is probably to just try to get some idea of what level of current different kinds of devices require, and judge your battery life expectancy accordingly. Anything that lights, heats, or turns a motor usually uses drains bats quickly - something like a small radio may run forever on one set of bats. Link to comment Share on other sites More sharing options...
Members stratocasterFIL Posted March 30, 2009 Members Share Posted March 30, 2009 I usually just use my multimeter for testing the voltage on batteries....works pretty well Link to comment Share on other sites More sharing options...
Members Belva Posted April 1, 2009 Members Share Posted April 1, 2009 I usually just use my multimeter for testing the voltage on batteries.... works pretty well Link to comment Share on other sites More sharing options...
Members UMT Posted April 1, 2009 Author Members Share Posted April 1, 2009 But isn't the problem with testing with a multimeter is that it will tell you how much juice the battery is putting out but not how much is left? If I'm wrong, please explain how to use a multimeter to test how much charge is left. Thanks! UMT Link to comment Share on other sites More sharing options...
Members musicdog400 Posted April 1, 2009 Members Share Posted April 1, 2009 Putting a voltmeter on a battery is next to no load, in the mega ohms. That won't tell you much. Put a 100 ohm resistor across it and then look at the volt meter. Link to comment Share on other sites More sharing options...
Members mike42 Posted April 2, 2009 Members Share Posted April 2, 2009 We're probably running this into the ground, but it's an interesting issue, and I suppose it could be very complex or pretty simple, depending on how you see it. Seems to me the OP is on the right track with his meter question. After a lot of years of flying RC airplanes, and being involved in other activities with various kinds of battery packs, I'm aware of any number of dedicated battery testers that do in fact work pretty well. But, they're all designed to be used in a specific application with specific kinds of bat packs. To expect a generic, one-size-fits-all tester, to really give you much meaningful information about battery capacity just doesn't seem realistic. It's a little like saying "I have a gallon of gas", now - is that a little or a lot? If you're going to use it in your weedeater it's probably a lot, but if you're putting it in your Hummer, not so much. Unless your tester is calibrated for a specific load to fit the expected use, or unless you know something about the current drain on the device that your using the bats in, the information just doesn't tell you much. I certainly agree with Musicdog that some kind of load on the bat if your checking with a multimeter, will give a more realistic indication, but even that is kind of shooting in the dark. Link to comment Share on other sites More sharing options...
Members ndog Posted April 2, 2009 Members Share Posted April 2, 2009 Somebody probably makes a battery analyzer that uses the voltage discharge versus time under load to determine the fitness of the battery. It'd make a neat project but sounds like overkill. The other suggestions make more sense. Link to comment Share on other sites More sharing options...
Members FredZepplen Posted April 2, 2009 Members Share Posted April 2, 2009 Sounds to me like your flashlight is already a dandy battery tester. When I was in school, one of the things we did was measure the internal resistance of a voltage source. In the end, the Prof posed us a question. Does a battery discharge or does its internal resistance slowly climb to infinity? Link to comment Share on other sites More sharing options...
Members WRGKMC Posted April 2, 2009 Members Share Posted April 2, 2009 With a standard meter a New battery reads about 1.7v. When the batteries just about had it it will read 1.2 to 1.4 volts. How long it lasts after that is usually a steep drop. A light type tester isnt as accurate as a good meter and neither is going to determine how long the load will take to completely discharge it. Once the acid has done its job its all over on disposables. This is where I'm a big believer in rechargables. For nearly the same cost you may get 20 or so usages out of the same battery. Link to comment Share on other sites More sharing options...
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