On 5/6/2013 1:31 PM, 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?

I've not seen that, but - digital VOM attached - I've seen a new/under full
replacement warranty standard 12V car battery intermittently become a 6V
battery, engine running & engine off, battery connected to the system. The
vehicle wouldn't run in "6V mode." It took some persuasion for the lady owner
of the vehicle to get the chain to honor their battery warranty, but her
vehicle hasn't suffered a "mystery engine stoppage" since flaky battery
replacement several years ago.

Bob W.