So here is the question ... why on earth would the Wall Wart transformer describe itself as "12v 0.5a", when in reality it is transformer with much higher output voltage?
So I set my Buck Converter (more of a cheap Bench PS really) to "12v 0.5a" and tried to charge them. But no matter how long I charged the cell, the Pack's charge indicator light would never go green
Because the 12V is produced when 0.5A is being drawn. These are known as unregulated supplies and used to be quite common but are now becoming a rarity.That is because it was a good regulator and 12V is not sufficient to charge a Lead / Acid battery.
So in this case < than 0.5A is likely to be being drawn at a higher voltage ?
I have never come across this before.
I was always told - never use a higher voltage than indicated.
Yes that is the case.You probably have not been about too long either, it was very common 30 years ago. These things are normally heavy due to the transformer.Good advice in the right place, but battery charging is different. If you think you can charge a 12V battery with a 12 supply then you are wrong.
Electronics appears to be full of non-absolutes :-)