We are building a new house and going with tankless gas water heater. I know bosch has one that ignites with water flow(no electricity) and Rinnai offers a back battery, I think we are putting in a Rheem. Can't find info online about them offering a backup pack. My issue-every year or two we lose power for 2-10 days. Ice storms, tornados or what ever else mother nature decides to throw at us in NE AR. I want to be able to have hot water!! Can you get a manual ignition like on gas fireplace logs for when to power goes out. Or should I switch to one of the above mentioned brands? Plumber chose Rheem. Need to get this figured out pretty quick. Any info would be greatly appreciated!