atom12, I finally had a chance today to run some tests.
I hooked up a pair of Sanken COS-11Ds to my Tascam DR-70D recorder, plugged in fresh batteries and ran it until it popped up the low battery warning.
Using a just charged set of Powerex MHRAA4 Rechargeable AA NiMH Batteries (1.2V, 2400mAh), I got 2 hr. 45 min. of record time.
These were brand new batteries so there's a chance that they might run a bit longer after I exercise them a few times but you get the idea.