Nick, my buying criterion has always been 30 hours of battery operation though in fact I haven't used that much yet. With the PMD660 that would mean about 16 or 20 AA's, which is not that bad. (4 HQ NIMH inside the unit, 12 spares in a carrying case, and a couple 4-packs of alkalines in reserve). But I -do- find the 7 hour internal capacity to be a limitation. The battery gauge is not very accurate so I can never tell when the internal cells are going flat, and it means I have to either hot swap or stop recording at some inconvenient time. Yes the sessions I record are frequently much longer than 7 hours. So I do want to put some kind of hot swap solution together. But it's not terribly urgent, and as mentioned, I feel likely to get an R-09 or some successor to it, so I don't want to put a lot more funds or energy into PMD660 improvements.