Well I finally had time to do a little testing on the WalMart battery.
AKG 483 > Oade ACM Marantz PMD-671 (24/48), phantom on, display light on.
I filled up 2 4GB CF cards + 12 minutes into the third before the last green light went out. So roughly 8 hours of run time.
It finally died 18 minutes later, saving the recording. All of this with a two year old battery, one that's been used a LOT!