The analyzer was about 5 years old, and well out of warranty, the battery is user replaceable using a common 9 volt battery. I tested the battery with a digital volt meter prior to return and it was above 9 volts, the display did illuminate at that time, but as mentioned it would not calibrate.
I have no idea if the manufacturer checked the battery, their reply just said it was completely dead when they tried it. As indicated I had already paid over $130 for a replacement O2 sensor, they offered to discount a new unit by that amount since they presumably could not repair mine, the price they wanted for a new one was so high however I felt I was not getting any consideration whatsoever. (Well above retail at local shops and online)
The Oxy Cheq I purchased to replace the anyalyzer was only $50 more than the price they wanted for exchange, and replacement O2 sensors for it are half the price of those for the O2EII. So far it functions perfectly, future customer service is still of course anyones guess.