[acanthicus]

If I understand you correctly, the readers work fine with the old replacements (some years old), but not with the new replacements. I use them every day. I wanted to replace them again, because the battery live decreases and those batteries are easy and relatively cheap to buy. Battery change is easy in 650 and 350, very tricky in 505.
The problem is, that the new batteries will not charge. The reader says something about it overheating. That is because the new batteries have the wrong thermistor, whatever that is... Based on the info I found in the internet, they use a standard thermistor and Sony used a special one. So the new battery delivers a wrong temperature to the reader, which stops the charging.

edit: this problem occurs with 650 and 350. I did not try to change the battery in the 505 a second time (because tricky...)