Jerry, yeah I am guessing you don't flip the batteries. I do this every watering hole. Even somewhat cloudy water is fine if it is treated twice. Like anything else, with an electronic switch, there is a delay for it to register the button press. It registers the change in current as an instruction to do something. Flipping the batteries will preserve them by reming ALL current drain. It takes 15-30 seconds to reinitialize the on board computer, though the lights are on. The button didn't seem to work. I don't usually notice it. But a couple times, I was trying to be efficient and did this step last. Again, it didn't work. I tried a couple times... I confirmed that this was the case at home. It took about 15sec at 65F. I am guessing somewhat longer in the cold fall weather. I am guessing there might also be differences in gadgets, too.
Being a simple device I would expect faster response from the thing. But, because it reinitializes, you cannot press the botton during this time. It will confuse it and seem to fail. Remove the batteries for a half minute, put them back in and wait.
As far as consumption goes, I get about 5-8 pints out of a set of rechargables. Unacceptable. For lithium batteries (and the hugher voltage) I get about 35-40 pints. There is a difference between the stated ~50 liters and actual usage. I have NEVER gotten more than 40 uses. 20% is a lot...but, it is closer to 50 than 0, I am fairly sure that is their advertising people with rounded numbers playing "SELL IT, SELL IT..." to eachother with QC taking the hit.
I do not personnaly feel that tis is a true problem. I do not believe most advertising, or, expect less because they lie. So, your course of action is a good one. Return it if it doesn't meet spec. Demand another. Then, in turn return it if it doesn't meet spec...really. Unless you can afford a big shot lawer and have spare dollars to burn, Spending $5 on shipping will be the only thing you can do.
That said, I like the UV for short trips. The packaging and electronics really SUCKS. But, the mUV is no better. It has minor issues(battery charge) and is subject to breakage. Just hook it up to a battery after ten or twenty liters...it will report charging all day, but work fine. ???