This product was purchased just prior to a trip to Vietnam and Thailand. I ran into a bit of frustration initially but discovered that it a very usable product. Initially I had some false "low battery" warnings. I discovered that 1) assuring the battery "cap" was properly aligned before tightening, and 2) if I get the low battery warning flashes, I'll loosen the cap and retighten, completely dry the pen and start over. Takes 30 secs. and works ever time. I've been very pleased with the product and feel like it was a good investment for treating questionable water sources. Can't wait to use it on a backpacking trip. I'm using only rechargeable nickel cadmium batteries bases on reviews I had read before purchasing mine and have been very pleased with them.