Hello:
I thought I would put in my 2 cents here on a few points:
As far as battery life with external mics (sorry for stating the obvious), it will depend greatly on the specific mics you are using (some draw far more current than others) and the current capacity of the AA you are using. For example, with AT4050 side address studio mics, I got about 3 hours run time using the internal Lithium battery only. I had the 2700mAh batteries on board just in case, but didn't need them.
As far as sound quality, I prefer the Tascam overall, especially when you consider the built in mics. This page has some samples we made comparing the built in mics with some external mics. Yes, the external mics sounded better, but I think it shows that the built in mics are pretty decent:
http://www.soundprofessionals.com/cgi-bin/gold/item/TAS-DR-100Hope this helps!
Best Regards,
Chris Carfagno
sales@soundprofessionals.com
www.soundprofessionals.com
The Sound Professionals, Inc.
3444 Sylon Blvd
Hainesport NJ, 08036
800-213-3021
609-267-4400
609-267-0054 fax