fawkes, i wonder the same thing as that is the type i want.
I ordered one from the folks that the link in the article points to. I will post the answer once I know how it operates.
I have a battery powered unit that I bought some many years ago - but I have to add it to the tank and turn it on. Frankly, I don't know if I have a need, but it will be handy to have around. You just never know when you will need something in a pinch. I recently took an unused 500 va UPS from a computer system and I run my two recirculation pumps from that. I haven't tested run time, but I am hoping it will last a couple of hours - there isn't much demand from the two pumps. I just need enough time to get the generator running. I am the second to last house on the electric run out in the country. I have to plan on being on the low end of the totem pole.