VARTA Battery :
I am sad to say that the poor battery did not survive the night.
IIRC I started discharging it at 2AM last night. I just woke up, 12H45, so about 10+ hours, immediately checked on the battery.... only to find voltage was down to.... 7 V ? No... well below that.... which is still a massive understatement.... voltage was down to.... 0.8V !!
Rob I am so sorry, I failed to protect this battery from under voltage.... I am a failure....
That said... even at 0.8V believe it or not, it was still spitting out a sizable current, 1mA !!
After 5 minutes or so, battery recovered a bit and unloaded voltage went up to 2.5V.... which from memory was also the voltage it read after its 30 years of storage when I dug it out the other day !
So I guess this battery "likes" this particular voltage...
So what to do now...
First I would like to not over dramatize the fact that I let it go flat.... because it had already been flat for 30 years, so I probably didn't do any more damage than had already been done, eh ?
Also, the fact it was still putting out 1mA at only 0.8V means, to me at least, that it's a warrior, it wants to live...
So I think I will charge it again, using Wilson. Slow C/10 again.
Then will do another discharge cycle, but this time I will conduct the experiment during the day, so that I can keep an eye on it regularly, from beginning to end, and will take note of precise start time, and time stamp for every voltage and current check I do.
Would be easier if I could do it automagically with a GPIB setup and some clever S/W on a computer... but alas the lab is nowhere near as sophisticated for now ! It's my plan for it be, though...
Also, since I have plenty of real estate on the bread board, I could add a comparator chip and a little miniature relay to automatically disconnect the battery when it reaches a certain voltage threshold. That would be neat.
The saga continues....