[kalee20]

I believe batteries were characterised generally at the 10-hour rate. Now 90mA for 10 hours is 0.9AH, so as 50mA is less current than this, I'd expect to get a bit better than 0.9AH.

However, for grid bias use, current drain is very low and I would have thought the manufacturer would be aiming to maximise shelf-life, rather than capacity (maybe smaller quantities of chemicals and zinc, but of a higher purity, so 'side reactions' are minimised and shelf-life increased, even though total Joules of energy are lowered).