Battery Tester's Readings Fluctuate - Page 1
Forum section: electronics / general

author: Boris_yo
author_rank: Frequent Contributor
timestamp: November 19, 2021, 10:29:32 am
content: Hello,Why battery tester's readings fluctuate? I bought it over a decade ago. Since it didn't fall down, could contacts degrade?https://streamable.com/rk3yp2Tested lithium AAA battery and it seems okay but when attempted testing rechargeable AA readings started going back and forth.

author: electr_peter
author_rank: Unknown
timestamp: November 19, 2021, 11:55:05 am
content: Not familiar with this type of battery testers. It seems they have no internal battery and uses test battery as a source for display. White battery may be too discharged - with low output voltage and high internal resistance, that may be not enough to light display properly.Or connection is bad somewhere.Do you have regular DMM to test voltages and compare? Is white battery any good otherwise (is it discharged)?

author: Boris_yo
author_rank: Frequent Contributor
timestamp: November 19, 2021, 03:41:29 pm
content: Actually I just wanted to test with multi-meter but one of probes got its cord torn out. Can it be fixed or to the trash it goes?

author: electr_peter
author_rank: Unknown
timestamp: November 19, 2021, 04:08:48 pm
content: It is difficult and not worthwile to repair, regular probes almost never break in this way. Much better option is to get new probes for DMM, pretty cheap item.You still could measure battery voltages with broken wire end.

author: Boris_yo
author_rank: Frequent Contributor
timestamp: November 19, 2021, 04:31:45 pm
content: Quote from: electr_peter on November 19, 2021, 04:08:48 pmIs black probe good with red probe from another set?I managed to measure and here is what I found:With multi-meter: voltage fluctuates between 1.22 - 1.23With battery tester: voltage fluctuates between 1.14 - 1.15My assumption is that multi-meter does not put load on battery while battery tester does.

author: tszaboo
author_rank: Super Contributor
timestamp: November 19, 2021, 04:39:46 pm
content: The tester loads the battery with a resistor.Your battery might be somewhat weak, or it's just the immediate voltage drop for a load.

author: tooki
author_rank: Super Contributor
timestamp: November 19, 2021, 07:00:35 pm
content: Quote from: Boris_yo on November 19, 2021, 10:29:32 amA rechargeable AA that starts at 0.95V is already basically empty. There’s practically no energy left in it, so any load just drags down the voltage. The fluctuation is likely due to the variable contact of the battery contacts. I bet if you squeezed on the contacts to give it a better connection, you’d get a more stable reading.I also expect that with a new battery, the voltage would remain much more stable.Quote from: Boris_yo on November 19, 2021, 04:31:45 pmYes, you can mix and match probes, but why? I can tell from the picture that those are very cheap probes. Do yourself a favor and get something a bit nicer.You are exactly right about the load: that’s what makes a battery tester a battery tester and not just a voltmeter. A battery tester applies a load so that you don’t get tricked by a no-load high voltage in a nearly dead battery, while a multimeter is designed to apply as little load as possible (so as to not affect the circuit under test).

author: Boris_yo
author_rank: Frequent Contributor
timestamp: November 20, 2021, 06:31:24 am
content: Quote from: tooki on November 19, 2021, 07:00:35 pmWhat is variable contact of the battery contacts?

author: Boris_yo
author_rank: Frequent Contributor
timestamp: November 20, 2021, 06:58:46 am
content: Quote from: tooki on November 19, 2021, 07:00:35 pmWhat makes quality probes better than cheap probes for home DIY? Are they more reliable when measuring mains voltage for example?