"the battery is not intended to be replaced"
That is the first thing that I've heard about an iFly that I don't like. Most current elecrtonic devices out-last their batteries. I'd hate to have to purchase a new unit in three years because the battery won't hold enough charge to be an effective back-up power source. I love the 720, and will carefully evaluate the 740, though the connectivity with the ELT, fuel gauges, etc. makes it really tempting.