Here is another little tid-bit on the PMD620...Using a pair of fresh Duracells, I got about seven hours of record time using the internal mics. Formatted the card, made some menu selections, then recorded an entire 4 GB card (6 hours 23 minutes at 16 bit/44.1 kHz), erased the file and started recording again (around 45 minutes). So not quite continuous recording time, but definitely continuous use...
I guess with mic plug-in, it would be quite a bit less; with line-in a bit more. With some nice rechargeables, I think you get a pretty long record time...