In the past, I have used both the 9v and 12v off a single Talentcell to power my MP6ii and an Oade mod Edirol UA-5 during the same recording.
I don't anymore, AND I have never had the following issue, but I have heard of ground hum being an issue when using the same battery for two devices. Again, never had the issue. To simply ease my mind, when I do decide to run the Edirol, I use a second, smaller Talentcell. More weight to the bag, yes, but only about a 1/2 lb of piece of mind for a problem I have never had.