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Q & A: batteries in series

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Most recent answer: 09/14/2014
Q:
Well I have to say even at my age i'm a bit of a novice where electricity is concerned so here's my issue. I have a battery power source that contains 6 Sub C 1.2v nigh batteries connected in series. The battery pack seems to have lost its power to hold a charge over the past six months. The batteries were manufactured in 2007. So I was interested to test the circuit for voltage and also test individual battery cells. I used a multimeter and tested the whole circuit by placing the + connector on the first positive battery connector then the - connector on the last negative battery. My reading was 5.5v. I tested each battery in sequence and each read at leas 1.35 v. so i'm having difficulty in understanding why the total battery output if measured in total only reads 5.5v and not something like 8.1 v ? your response would be greatly appreciated. Also each battery is rated at 1.2v so i'm confused as to why it should read 1.35v ? any response would be most welcome :-)
- Bruce Liron (age 54)
Philippines
A:

One part of your question is fairly easy. A fully charged battery typically has a bit higher voltage than the rating, with the difference depending on the battery type.

As for the voltage not equaling the sum of the voltages, that's very peculiar. One possibility is that there's a problem with your meter, that it has a much lower impedance than it should. Then it will draw significant current. The voltage on a battery drops as it supplies current, rather sharply if the current exceeds the limits of what the battery can supply. Of course the meter will draw more current at higher voltage, so that will have a bigger effect on the voltage of the batteries. Still, the effect you're seeing sounds suspiciously large. 

You might try another meter. You could also check to make sure that somehow the meter probes aren't touching somthing else which could carry current.

Mike W.

 

It sounds to me like one of the batteries was turned around backwards   4*1.35 = 5.4

LeeH


(published on 09/14/2014)

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