Poll
47%
53%
The Sum of the Power Cosmic versus the Sum of the Power Battery? I'd personally say draw as far as potency. You can't base it on the weilders because Surfer isn't the sum and Galactus, while embodying the power cosmic, has physical limitations, is never consistently depicted at full capacity, and uses a large amount of his personal power keeping Abraxus at bay.
I'd say they are interchangable, even given the Oan's powers supposed connection to the Source.