Interesting behavior from PowerSonic battery

On Monday, May 6, 2013 3:31:41 PM UTC-4, Steve Leonard wrote:
I have two 6 volt and one 2 volt PowerSonic cells in series to make a 14 volt pack for one of my sailplanes. I had one of the batteries go bad, so I did a little checking to see which one. All showed appropriate charge voltage when not loaded, however, one battery went from 6.2 volts no load, to showing -3.8 or so volts when loaded by turning on a S-Nav and GPS-Nav. Now, I have seen an individual battery go to very nearly zero volts, but never negative voltage! Turn everything off, and it slowly recovers back to showing about 6.2 volts no load.



Anyone else ever seen a battery do that before? And please, no comments about 14 volt battery packs or old technology batteries. Age of battery unknown, as I do not remember when I built up the pack.



Just curious.

Since you have all the batteries in series with the load the voltage drop across the bad battery it appears like the bad battery is being reverse-biased by the good ones. You would see the same kind of result if you replaced the bad battery with a resistor and measured the voltage across it. The bad battery obviously has what is called "High internal resistance".

-PC

On Monday, May 6, 2013 5:14:28 PM UTC-5, Jim wrote:
Since you have all the batteries in series with the load the voltage drop across the bad battery it appears like the bad battery is being reverse-biased by the good ones. You would see the same kind of result if you replaced the bad battery with a resistor and measured the voltage across it. The bad battery obviously has what is called "High internal resistance". -PC

Yep. And the guy at All Pack gave the battery the highly scientific "shake test". Apparently, the innerds dried up and came apart. Sounded like shaking a box of rocks. 5 years of service from the battery, and $23 to replace it in the pack. Will be good to be able to secure the battery in the intended box again rather than having a smaller one out on the shelf behind me.