I don't know what size the battery compartment in your 671 is, but you might want to try for more capacity. AllBattery.com is a good company, BTW, and has lots of different configurations of NiMH packs; you can even build your own to fit.
After years of being fed up with the crap OEM NiCads (6x AA NiCad pack rated at 1400mAh, list price $100), I finally crammed a 4600mAh NiMH pack (6x Sub-C cells, $28.00 from AllBattery) into my DA-P1. With minor surgery it only sticks out about 1/16", including the gaffer tape(!) It records approx. 5-6 hrs on the 4600mAh pack, which has more capacity, and only half the weight of the sealed lead-acid external pack I needed previously.
On the DA-P1, I just use the existing DC-In connector for internal charging.
Cheers
Dave